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  4. [Form 3] Keystone Acquisition Corp. Initial Statement of Beneficial Ownership

Keystone Acquisition (KEYYU) sponsor reports 9.48M Class B shares

Filing Impact
(Neutral)
Filing Sentiment
(Neutral)
Form Type
3

Rhea-AI Filing Summary

Keystone Acquisition Corp. filed an initial insider ownership report showing that Keystone International Acquisition Management LLC, managed by Jae Hyun (James) Park, directly holds 9,483,333 Class B ordinary shares. These Class B shares are convertible into the issuer’s Class A ordinary shares and have no expiration date.

The Class B shares beneficially owned include up to 1,250,000 shares that may be forfeited depending on how much of the underwriters’ over-allotment option is exercised in the company’s initial public offering of units.

Positive

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Insider Keystone International Acquisition Management LLC, Park Jae Hyun
Role Executive Chairman | null
Type Security Shares Price Value
holding Class B Ordinary Shares -- -- --
Holdings After Transaction: Class B Ordinary Shares — 9,483,333 shares (Direct, null)
Footnotes (1)
  1. The Class B ordinary shares are convertible for the Issuer's Class A ordinary shares as described under the heading "Description of Securities" in the Issuer's Registration Statement on Form S-1 (File No. 333-295539) (the "Registration Statement") and have no expiration date. The Class B ordinary shares beneficially owned by the Reporting Persons include up to 1,250,000 Class B ordinary shares subject to forfeiture to the Issuer depending on the extent to which the underwriters' over-allotment option is exercised in connection with the Issuer's initial public offering of units, as described in the Registration Statement. Keystone International Acquisition Management LLC is the record holder of the securities reported herein. Jae Hyun (James) Park is the managing member of Keystone International Acquisition Management LLC. Mr. Park has voting and investment discretion with respect to the securities held of record by Keystone International Acquisition Management LLC.
Class B shares held 9,483,333 shares Direct holdings reported on Form 3
Underlying Class A shares 9,483,333 shares Convertible from Class B ordinary shares
Shares subject to forfeiture 1,250,000 shares May be forfeited based on IPO over-allotment exercise
Conversion price <money>$0.0000</money> per share Exercise/conversion price shown for Class B into Class A
Class B ordinary shares financial
"The Class B ordinary shares are convertible for the Issuer's Class A ordinary shares as described under the heading"
Class B ordinary shares are a type of ownership stake in a company that typically come with different voting rights or privileges compared to other share classes. For investors, they represent a way to hold part of the company’s value and influence its decisions, often with fewer voting rights than Class A shares. Understanding these shares helps investors assess their level of control and potential returns within a company.
Class A ordinary shares financial
"The Class B ordinary shares are convertible for the Issuer's Class A ordinary shares as described under the heading"
Class A ordinary shares are a type of ownership stake in a company that typically grants voting rights to shareholders, allowing them to have a say in important company decisions. They often come with priority in receiving dividends or profits, making them attractive to investors seeking influence and potential income. These shares help distinguish different levels of ownership and rights within a company's stock structure.
over-allotment option financial
"subject to forfeiture to the Issuer depending on the extent to which the underwriters' over-allotment option is exercised"
An over-allotment option is a special agreement that allows underwriters to sell more shares than initially planned if demand is high. Think of it like a retailer offering extra units of a popular product to meet additional customer interest. This option helps ensure the full sale is completed and can also give investors extra shares if they want more.
beneficially owned financial
"The Class B ordinary shares beneficially owned by the Reporting Persons include up to 1,250,000 Class B ordinary shares"
Beneficially owned describes securities or assets where a person has the economic rights and control—such as the right to receive dividends and to direct voting—even if legal title is held in another name. Think of it like having the keys and using a car that’s registered to someone else: you get the benefits and make decisions. Investors care because beneficial ownership reveals who truly controls value and voting power, affecting corporate decisions and takeover dynamics.
Registration Statement on Form S-1 regulatory
"as described under the heading "Description of Securities" in the Issuer's Registration Statement on Form S-1"
A registration statement on Form S-1 is a detailed filing a company submits to the U.S. securities regulator to register new shares for public sale; it includes a plain-language prospectus, financial statements, business description and risk factors. For investors it matters because it provides the official, comprehensive blueprint of the offering — like an owner’s manual — allowing buyers to assess risks, inspect financial health and compare valuation before deciding to invest.
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SEC Form 3
FORM 3UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940
OMB APPROVAL
OMB Number:3235-0104
Estimated average burden
hours per response:0.5
1. Name and Address of Reporting Person*
Keystone International Acquisition Management LLC
(Last)(First)(Middle)
C/O KEYSTONE ACQUISITION CORP.
142 WEST 57TH STREET, 11TH FLOOR
(Street)
NEW YORK NEW YORK 10019
(City)(State)(Zip)
UNITED STATES
(Country)		2. Date of Event Requiring Statement (Month/Day/Year)
06/02/2026		3. Issuer Name and Ticker or Trading Symbol
Keystone Acquisition Corp. [ KEYY ]
3a. Foreign Trading Symbol
5. If Amendment, Date of Original Filed (Month/Day/Year)
4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
XDirectorX10% Owner
XOfficer (give title below)Other (specify below)
Executive Chairman
6. Individual or Joint/Group Filing (Check Applicable Line)
Form filed by One Reporting Person
XForm filed by More than One Reporting Person
Table I - Non-Derivative Securities Beneficially Owned
1. Title of Security (Instr. 4) 2. Amount of Securities Beneficially Owned (Instr. 4) 3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5) 4. Nature of Indirect Beneficial Ownership (Instr. 5)
Table II - Derivative Securities Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4) 2. Date Exercisable and Expiration Date (Month/Day/Year)3. Title and Amount of Securities Underlying Derivative Security (Instr. 4) 4. Conversion or Exercise Price of Derivative Security 5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5) 6. Nature of Indirect Beneficial Ownership (Instr. 5)
Date ExercisableExpiration DateTitleAmount or Number of Shares
Class B Ordinary Shares (1) (1)Class A Ordinary Shares9,483,333(1)D(2)
1. Name and Address of Reporting Person*
Keystone International Acquisition Management LLC
(Last)(First)(Middle)
C/O KEYSTONE ACQUISITION CORP.
142 WEST 57TH STREET, 11TH FLOOR
(Street)
NEW YORK NEW YORK 10019
(City)(State)(Zip)
UNITED STATES
(Country)
Relationship of Reporting Person(s) to Issuer
XDirectorX10% Owner
XOfficer (give title below)Other (specify below)
Executive Chairman
1. Name and Address of Reporting Person*
Park Jae Hyun
(Last)(First)(Middle)
C/O KEYSTONE ACQUISITION CORP.
142 WEST 57TH STREET, 11TH FLOOR
(Street)
NEW YORK NEW YORK 10019
(City)(State)(Zip)
UNITED STATES
(Country)
Relationship of Reporting Person(s) to Issuer
XDirectorX10% Owner
Officer (give title below)Other (specify below)
Explanation of Responses:
1. The Class B ordinary shares are convertible for the Issuer's Class A ordinary shares as described under the heading "Description of Securities" in the Issuer's Registration Statement on Form S-1 (File No. 333-295539) (the "Registration Statement") and have no expiration date. The Class B ordinary shares beneficially owned by the Reporting Persons include up to 1,250,000 Class B ordinary shares subject to forfeiture to the Issuer depending on the extent to which the underwriters' over-allotment option is exercised in connection with the Issuer's initial public offering of units, as described in the Registration Statement.
2. Keystone International Acquisition Management LLC is the record holder of the securities reported herein. Jae Hyun (James) Park is the managing member of Keystone International Acquisition Management LLC. Mr. Park has voting and investment discretion with respect to the securities held of record by Keystone International Acquisition Management LLC.
Remarks:
See Exhibit 99.1 - Joint Filer Information, which is incorporated herein by reference and describes in further detail the relationships of the Reporting Persons to the Issuer. See Exhibits 24.1 and 24.2 - Powers of Attorney.
/s/ Claudia Hanover, Attorney-in-Fact for Keystone International Acquisition Management LLC06/02/2026
/s/ Claudia Hanover, Attorney-in-Fact for Jae Hyun (James) Park06/02/2026
** Signature of Reporting PersonDate
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 5 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.
* Form 3: SEC 1473 (03-26)

Source: View Original Filing on SEC EDGAR

FAQ

What insider holdings does Keystone Acquisition Corp. (KEYYU) report on this Form 3?

The filing reports that Keystone International Acquisition Management LLC directly holds 9,483,333 Class B ordinary shares. These shares are beneficially owned by the reporting persons and are convertible into an equal number of Class A ordinary shares according to the company’s registration statement.

Who controls the reported shares in Keystone Acquisition Corp. (KEYYU)?

Keystone International Acquisition Management LLC is the record holder of the shares, and Jae Hyun (James) Park is its managing member. Mr. Park has voting and investment discretion over the securities held of record by the LLC, giving him effective control over these holdings.

How are Keystone Acquisition Corp. (KEYYU) Class B ordinary shares treated under the Form 3?

The Class B ordinary shares are described as convertible into Keystone Acquisition Corp.’s Class A ordinary shares, with no expiration date. Their terms are set out under “Description of Securities” in the company’s Form S-1 registration statement referenced in the footnotes.

What is the forfeiture risk on Keystone Acquisition Corp. (KEYYU) sponsor shares?

Up to 1,250,000 of the reported Class B ordinary shares are subject to forfeiture back to the issuer. This depends on the extent to which underwriters exercise their over-allotment option in connection with Keystone Acquisition Corp.’s initial public offering of units.

Does this Keystone Acquisition Corp. (KEYYU) Form 3 show any insider buying or selling?

The Form 3 functions as an initial ownership report and indicates a holding entry rather than a trade. The transaction data are categorized as a holding with an unknown transaction code, and summary fields show no buys, sells, or derivative exercises.