Boston Partners holds 5.23% of MasterBrand (NASDAQ: MBC)

Rhea-AI Filing Summary

Boston Partners filed Amendment No. 2 to a Schedule 13G/A reporting beneficial ownership of 5.23% of MasterBrand, Inc. common stock, equal to 6,669,808 shares as of 03/31/2026.

The filing states these shares are held by Boston Partners for the discretionary accounts of certain clients and notes that, by reason of Rule 13d-3, Boston Partners "may be deemed to be a beneficial owner". The filing indicates sole voting power for 6,272,359 shares and sole dispositive power for 6,669,808 shares. The amendment is signed by Ali Farooqi on 05/14/2026.

Insights

Institutional Ownership Analyst

Boston Partners reports a 5.23% passive holding in MasterBrand as of 03/31/2026.

The filing shows 6,669,808 shares held in discretionary client accounts with sole dispositive power and 6,272,359 shares of sole voting power. It is filed as an amendment to Schedule 13G/A and cites Rule 13d-3 attribution.

Holder decisions will determine future activity; timing and intended disposition policies are not disclosed in the excerpt.

Key Figures

Shares beneficially owned: 6,669,808 shares Percent of class: 5.23% Sole voting power: 6,272,359 shares +2 more

5 metrics

Shares beneficially owned 6,669,808 shares as of 03/31/2026

Percent of class 5.23% MasterBrand common stock as of 03/31/2026

Sole voting power 6,272,359 shares reported voting power in Schedule 13G/A

Sole dispositive power 6,669,808 shares reported dispositive power in Schedule 13G/A

Signature date 05/14/2026 Amendment signed by Ali Farooqi

Key Terms

Schedule 13G/A, beneficially owned, Rule 13d-3

3 terms

Schedule 13G/A regulatory

"This Schedule is being filed with respect to 6,669,808 shares"

A Schedule 13G/A is an amended public filing with the U.S. securities regulator that updates a previous Schedule 13G, disclosing when an individual or group holds a substantial (typically over 5%) stake in a company and is claiming a passive, non‑controlling intent. Investors monitor these updates because rising or falling holdings can signal changing confidence, potential future moves, or shifts in voting power — like watching a public ledger where large shareholders quietly adjust their positions.

beneficially owned financial

"Amount beneficially owned: 6,669,808"

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.

Rule 13d-3 regulatory

"By reason of rule 13d-3 under the act Boston Partners may be deemed"

Rule 13d-3 defines who is treated as the beneficial owner of a company’s shares for U.S. securities disclosure rules — essentially anyone who has the power to vote or direct how shares are voted, or the power to buy or sell them, even if they don’t hold the certificates. For investors this matters because crossing certain ownership thresholds triggers public filing and disclosure obligations and signals potential control or influence, much like having the keys to a car implies you can drive it even if it’s registered to someone else.

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SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 2)

MasterBrand, Inc.

(Name of Issuer)

Common Stock

(Title of Class of Securities)

57638P104

(CUSIP Number)

03/31/2026

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

schemaVersion:

SCHEDULE 13G

CUSIP Number(s): 57638P104

1

Names of Reporting Persons

Boston Partners

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 6,272,359.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 6,669,808.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

6,669,808.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

5.23 %

12

Type of Reporting Person (See Instructions)

IA

SCHEDULE 13G

Item 1.
(a)	Name of issuer: MasterBrand, Inc.
(b)	Address of issuer's principal executive offices: 3300 ENTERPRISE PARKWAY, SUITE 300, BEACHWOOD, OHIO 44122
Item 2.
(a)	Name of person filing: Boston Partners
(b)	Address or principal business office or, if none, residence: ONE BEACON STREET 30TH FLOOR BOSTON, Massachusetts 02108
(c)	Citizenship: Boston Partners - DELAWARE
(d)	Title of class of securities: Common Stock
(e)	CUSIP No.: 57638P104
Item 3.	If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)	Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)	Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)	An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)	An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)	A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)	A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution:
(k)	Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.	Ownership
(a)	Amount beneficially owned: 6,669,808
(b)	Percent of class: 5.23 %
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: Boston Partners - 6,272,359
	(ii) Shared power to vote or to direct the vote: Boston Partners - 0
	(iii) Sole power to dispose or to direct the disposition of: Boston Partners - 6,669,808
	(iv) Shared power to dispose or to direct the disposition of: Boston Partners - 0
Item 5.	Ownership of 5 Percent or Less of a Class.
	Not Applicable
Item 6.	Ownership of more than 5 Percent on Behalf of Another Person.
	If any other person is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, such securities, a statement to that effect should be included in response to this item and, if such interest relates to more than 5 percent of the class, such person should be identified. A listing of the shareholders of an investment company registered under the Investment Company Act of 1940 or the beneficiaries of employee benefit plan, pension fund or endowment fund is not required. This Schedule is being filed with respect to 6,669,808 shares of Master Brand, Inc. (the Common Stock) held by Boston Partners on 03/31/2026 for the discretionary account of certain clients. By reason of rule 13d-3 under the act Boston Partners may be deemed to be a beneficial owner of such Common Stock. To the knowledge of Boston Partners no person has the right to receive or the power to direct the receipt of dividends from or the proceeds from the sale of such Common Stock which represents more than 5% of the outstanding shares of the Common Stock referred to in item 4(b) hereof.
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	Not Applicable
Item 8.	Identification and Classification of Members of the Group.
	Not Applicable
Item 9.	Notice of Dissolution of Group.
	Not Applicable

Item 10.

Certifications:

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Boston Partners

Signature:	/s/ Ali Farooqi
Name/Title:	Ali Farooqi / Senior Compliance Manager
Date:	05/14/2026

FAQ

What stake does Boston Partners report in MasterBrand (MBC)?

Boston Partners reports beneficial ownership of 6,669,808 shares, equal to 5.23% of MasterBrand common stock as of 03/31/2026. The shares are held in discretionary client accounts.

Does Boston Partners have voting control over the shares?

The filing shows sole voting power for 6,272,359 shares and sole dispositive power for 6,669,808 shares, indicating voting authority for most of the reported position as of 03/31/2026.

Is Boston Partners deemed the beneficial owner under SEC rules?

The amendment states Boston Partners "may be deemed to be a beneficial owner" under Rule 13d-3. The filing attributes the position to Boston Partners for discretionary client accounts rather than to a single third party.

When was the Schedule 13G/A amendment signed?

The amendment is signed by Ali Farooqi, Senior Compliance Manager and dated 05/14/2026. The reported ownership amount is effective as of 03/31/2026.

Are these shares held for Boston Partners or clients?

The filing specifies the 6,669,808 shares are held by Boston Partners "for the discretionary account of certain clients," indicating client-directed holdings under Boston Partners' management.