MITSUI SUMITOMO INSURANCE CO LTD - 04 Mar 2026 SCHEDULE 13D/A Report for W. R. BERKLEY CORPORATION Common Stock, par value $0.20 per share (WRB)

Filing manager: MITSUI SUMITOMO INSURANCE CO LTD
Reporting owner: Mitsui Sumitomo Insurance Co., Ltd.
Security: W. R. BERKLEY CORPORATION Common Stock, par value $0.20 per share
Beneficially owned shares: 58,780,450 shares
Large-stake signal: Form
SCHEDULE 13D/A
Active or control-oriented beneficial ownership filing.
Ownership
16%
Beneficial ownership of this reported class.
Shares
58,780,450 shares
Shares beneficially owned as disclosed.
Event date
04 Mar 2026
Date tied to the ownership event or amendment.
Accepted by SEC
05 Mar 2026
EDGAR acceptance date.
How to read this large-stake filing
Schedule 13D/G filings focus on beneficial ownership stakes, not a full portfolio.
Compare this filing with the holder history and issuer page before treating the percentage as a current position.
Use amendments to understand whether the disclosed stake increased, decreased, or changed reporting status.
Class ownership: 16%
Symbol: WRB
Shares outstanding: 374,397,771 shares
SEC form: SCHEDULE 13D/A
Accepted by SEC: 05 Mar 2026, 07:00:04 UTC
Event date: 04 Mar 2026
Prior SEC filing: 06 Feb 2026
Source filing: View source filing

Key filing fact

MITSUI SUMITOMO INSURANCE CO LTD disclosed 16% ownership in W. R. BERKLEY CORPORATION Common Stock, par value $0.20 per share (WRB) on 04 Mar 2026.

Key facts

MITSUI SUMITOMO INSURANCE CO LTD filed SCHEDULE 13D/A for W. R. BERKLEY CORPORATION Common Stock, par value $0.20 per share (WRB).
Disclosed ownership: 16%.
Date of event: 04 Mar 2026.

This page turns one Schedule 13D/G filing into a quick large-stake read before the raw reporting-person rows.
Use the linked SEC filing as the source of truth for ownership percentages, shares, and reporting-party details.

Backed by Schedule 13D/13G

Beneficial ownership values are sourced from the original SEC Schedule 13D/13G filing.

Reporting persons

Names, ownership percentages, voting power, signatures, titles, and CIKs as disclosed in this Schedule 13D/G filing.

Name	Ownership	Shares owned	Sole voting power	Shared voting power	Signature	Title	CIK
Mitsui Sumitomo Insurance Co., Ltd.	16%	58,780,450	58,780,450	0	/s/ Hironori Morimoto	Hironori Morimoto/Authorized Signatory	0001142206
MS&AD Insurance Group Holdings, Inc.	16%	58,780,450	0	58,780,450	/s/ Hironori Morimoto	Hironori Morimoto/Authorized Signatory	0001431048

CIK / CUSIP context first

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