MITSUI SUMITOMO INSURANCE CO LTD - 04 Dec 2025 SCHEDULE 13D 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: 48,601,588 shares
Large-stake signal: Form
SCHEDULE 13D
Active or control-oriented beneficial ownership filing.
Ownership
13%
Beneficial ownership of this reported class.
Shares
48,601,588 shares
Shares beneficially owned as disclosed.
Event date
04 Dec 2025
Date tied to the ownership event or amendment.
Accepted by SEC
11 Dec 2025
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: 13%
Symbol: WRB
Shares outstanding: 379,699,906 shares
SEC form: SCHEDULE 13D
Accepted by SEC: 11 Dec 2025, 17:03:26 UTC
Event date: 04 Dec 2025
Next SEC filing: 14 Jan 2026
Source filing: View source filing

Key filing fact

MITSUI SUMITOMO INSURANCE CO LTD disclosed 13% ownership in W. R. BERKLEY CORPORATION Common Stock, par value $0.20 per share (WRB) on 04 Dec 2025.

Key facts

MITSUI SUMITOMO INSURANCE CO LTD filed SCHEDULE 13D for W. R. BERKLEY CORPORATION Common Stock, par value $0.20 per share (WRB).
Disclosed ownership: 13%.
Date of event: 04 Dec 2025.

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.	13%	48,601,588	48,601,588	0	/s/ Hironori Morimoto	Hironori Morimoto/Authorized Signatory	0001142206
MS&AD Insurance Group Holdings, Inc.	13%	48,601,588	0	48,601,588	/s/ Hironori Morimoto	Hironori Morimoto/Authorized Signatory	0001431048

CIK / CUSIP context first

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