Ownership Submission
FORM 4
Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940
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(Print or Type Responses)
1. Name and Address of Reporting Person *
WHITE MOUNTAINS INSURANCE GROUP LTD
  2. Issuer Name and Ticker or Trading Symbol
MONTPELIER RE HOLDINGS LTD [MRH]
5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
_____ Director __X__ 10% Owner
_____ Officer (give title below) _____ Other (specify below)
(Last)
(First)
(Middle)
80 SOUTH MAIN STREET
3. Date of Earliest Transaction (Month/Day/Year)
03/08/2005
(Street)

HANOVER, NH 03755
4. If Amendment, Date Original Filed(Month/Day/Year)
6. Individual or Joint/Group Filing(Check Applicable Line)
_X_ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person
(City)
(State)
(Zip)
Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3)
2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code
(Instr. 8)
4. Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5)
5. Amount of Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 3 and 4)
6. Ownership Form: Direct (D) or Indirect (I)
(Instr. 4)
7. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V Amount (A) or (D) Price
Common Shares 03/08/2005   J(1)   3,063 A $ 41.78 9,189 I By Folksamerica Reinsurance Company (2)
Common Shares               3,600,000 I By OneBeacon Insurance Company (2)
Common Shares               900,000 I By OneBeacon Insurance Group LLC (2)
Common Shares               1,800,000 I By Pennsylvania General Insurance Company (2)

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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security
(Instr. 3)
2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (Month/Day/Year) 3A. Deemed Execution Date, if any (Month/Day/Year) 4. Transaction Code
(Instr. 8)
5. Number of Derivative Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4, and 5)
6. Date Exercisable and Expiration Date
(Month/Day/Year)
7. Title and Amount of Underlying Securities
(Instr. 3 and 4)
8. Price of Derivative Security
(Instr. 5)
9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 4)
10. Ownership Form of Derivative Security: Direct (D) or Indirect (I)
(Instr. 4)
11. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares
Warrant Shares $ 16.67 (3)               (4) 01/03/2012 Common Shares 7,172,357.5   7,172,357.5 I By wholly-owned subsidiaries of White Mountains Insurance Group, Ltd. See Footnote 5. (5)

Reporting Owners

Reporting Owner Name / Address Relationships
 Director  10% Owner  Officer  Other
WHITE MOUNTAINS INSURANCE GROUP LTD
80 SOUTH MAIN STREET
HANOVER, NH 03755
    X    

Signatures

 Dennis Beaulieu, Corporate Secretary, White Mountains Insurance Group, Ltd.   03/08/2005
**Signature of Reporting Person Date

 Dennis Beaulieu, by Power of Attorney on behalf of Folksamerica Reinsurance Company   03/08/2005
**Signature of Reporting Person Date

 Dennis Beaulieu, by Power of Attorney on behalf of OneBeacon Insurance Group, LLC, OneBeacon Insurance Company, and Pennsylvania General Insurance Company   03/08/2005
**Signature of Reporting Person Date

 Dennis Beaulieu, by Power of Attorney on behalf of White Mountains Holdings Bermuda Ltd.   03/08/2005
**Signature of Reporting Person Date

 Dennis Beaulieu, by Power of Attorney on behalf of Sirius International Insurance Corporation   03/08/2005
**Signature of Reporting Person Date

 Dennis Beaulieu, on behalf of White Mountains Financial Services Ltd.   03/08/2005
**Signature of Reporting Person Date

Explanation of Responses:

* If the form is filed by more than one reporting person, see Instruction 4(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).
(1) Pro rata distribution from Century Capital Partners LP, of which Folksamerica Reinsurance Company, an indirect wholly-owned subsidiary of White Mountains Insurance Group, Ltd., is a limited partner.
(2) Folksamerica Reinsurance Company, OneBeacon Insurance Company, The Camden Fire Insurance Association, and Pennsylvania General Insurance Company are indirect wholly-owned subsidiaries of White Mountains Insurance Group, Ltd.
(3) Warrants Shares are exercisable for Common Shares on a 1 for 1 basis at an exercise price of $16.67 per Warrant Share.
(4) Currently exercisable.
(5) Warrant Shares are held by Folksamerica Reinsurance Company, White Mountains Holdings Bermuda Ltd., Sirius International Insurance Corporation and White Mountains Financial Services Ltd., each an indirect wholly-owned subsidiary of White Mountains Insurance Group, Ltd.

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