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                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549


                                  SCHEDULE 13G



                    UNDER THE SECURITIES EXCHANGE ACT OF 1934



                          Aspen Insurance Holdings Ltd.
            ---------------------------------------------------------
                                (Name of Issuer)


                Ordinary Shares, $0.15144558 par value per share
  ----------------------------------------------------------------------------
                         (Title of Class of Securities)


                                   G05384 10 5
                         ------------------------------
                                 (CUSIP Number)



                                December 31, 2004
                  ---------------------------------------------
             (Date of Event Which Requires Filing of this Statement)

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

[ ] Rule 13d -1 (b)

[ ] Rule 13d - 1(c)

[X] Rule 13d - 1(d)

The information required in the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).


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CUSIP No.G05384 10 5

    1   Name of Reporting Persons.
        I.R.S Identification Nos. of above persons (entities only).
        Montpelier Reinsurance Ltd.

    2   Check the Appropriate Box if a Member of a Group

        (a)

        (b)

    3.  SEC Use Only

    4   Citizenship or Place or Organization     Bermuda

Number of Shares       5.  Sole Voting Power: 4,000,000*
Beneficially
Owned by Each          6.  Shared Voting Power: 0
Reporting Person
With:                  7.  Sole Dispositive Power:  4,000,000

                       8   Shared Dispositive Power: 0

    9.  Aggregate Amount Beneficially Owned by Each Reporting Person
        4,000,000**

    10. Check if the Aggregate Amount in Row (9) Excludes Certain Shares

    11  Percent of Class Represented by Amount in Row (9) 5.8%*

    12. Type of Reporting Person: CO



    *  See Item 4 (b) below.

    ** See Item 4 (a) below.

    


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ITEM 1.

     (a) Name of Issuer: Aspen Insurance Holdings Limited (the "Company")

     (b) Address of Issuer's Principal Executive Offices:

         Victoria Hall
         11 Victoria Street
         Hamilton HM 11
         Bermuda

ITEM 2.

     (a) Name of Person Filing: Montpelier Reinsurance Ltd., a wholly-owned
     subsidiary of Montpelier Re Holdings Ltd.

     (b) Address of Principal Business Office or, if none, Residence:

         Mintflower Place
         8 Par-La-Ville Road
         Hamilton HM 08
         Bermuda

     (c) Citizenship: Bermuda

     (d) Title of Class of Securities: Ordinary Shares, par value, $0.15144558

     (e) CUSIP Number: G05384 10 5

ITEM 3.  If this statement is filed pursuant to Sections 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 Section
         240.13d-I(b)(1)(ii)(E);

(f)  [ ] An employee benefit plan or endowment fund in accordance with Section
         240.13d-I(b)(1)(ii)(F);

(g)  [ ] A parent holding company or control person in accordance with Section
         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)  [ ] Group, in accordance with Section 240.13d-l(b)(1)(ii)(J).

ITEM 4. OWNERSHIP.

         (a) Amount beneficially owned: As of December 31, 2004, Montpelier
         Reinsurance Ltd. beneficially owned 4,000,000 ordinary shares of the
         Company. On February 4, 2005, Montpelier Reinsurance Ltd. sold
         1,500,000 ordinary shares of the Company. Accordingly, Montpelier
         Reinsurance Ltd. beneficially owns 2,500,000 ordinary shares of the
         Company as of the date hereof.


         (b) Percent of class: As of December 31, 2004, Montpelier Reinsurance
         Ltd. beneficially owned 5.8% of the ordinary shares of the Company. As
         a result of the transaction described above, Montpelier


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         Reinsurance Ltd. beneficially owns approximately 3.6% of the ordinary
         shares of the Company as of the date hereof.

         In general, except as provided in the Company's Bye-laws, shareholders
have one vote for each ordinary share held by them and are entitled to vote at
all meetings of shareholders. The Company's Bye-laws provide, among other
things, that if, and so long as the ordinary shares of a shareholder in the
Company are treated as "controlled shares" (as defined below) of any U.S. Person
and such controlled shares constitute 9.5% or more of the votes conferred by the
issued shares of the Company, then the voting rights with respect to the
controlled shares owned by such U.S. Person shall be limited, in the aggregate,
to a voting power of less than 9.5%, under a formula specified in the Company's
Bye-laws. "Controlled shares" means, among other things, all ordinary shares
that a U.S. Person is deemed to beneficially own, directly, indirectly, or
constructively (within the meaning of Section 958 of the United States Internal
Revenue Code of 1986, as amended). The Bye-laws of the Company also allocate
voting power of U.S. Persons with voting power in excess of 9.5% to other
shareholders. Therefore, because the Reporting Person is not a U.S. Person, the
Reporting Person may have voting rights in excess of one vote per ordinary
share. The precise voting power of the Reporting Person will be determined by
the Company at the time of any shareholder vote, taking into account the
necessary voting adjustments described above based on the overall shareholder
base at the time.

         (c) Number of shares as to which the person has:

                (i)    Sole power to vote or to direct the vote: See
                       response to Item 5 on page 2.

                (ii)   Shared power to vote or to direct the vote: See
                       response to Item 6 on page 2.

                (iii)  Sole power to dispose or to direct the disposition of:
                       See response to Item 7 on page 2.

                (iv)   Shared power to dispose or to direct the disposition of:
                       See response to Item 8 on page 2.

ITEM 5.  OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS

         If this statement is being filed to report the fact that as of the date
         hereof the reporting person has ceased to be the beneficial owner of
         more than five percent of the class of securities, check the 
         following. [X]

ITEM 6.  OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON.

         N/A

ITEM 7.  IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED THE
         SECURITY BEING REPORTED ON BY THE PARENT HOLDING COMPANY

         N/A

ITEM 8.  IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP

         N/A.

ITEM 9.  NOTICE OF DISSOLUTION OF GROUP

         N/A.

ITEM 10. CERTIFICATION

(a)      N/A

(b)      N/A.


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                                   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.

                                                  February 11, 2005
                                       ---------------------------------------
                                                        Date

                                                /s/ Jonathan B. Kim
                                       ---------------------------------------
                                                     Signature

                                          Jonathan B. Kim / General Counsel
                                       ---------------------------------------
                                                      Name/Title


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