Exhibit 10.45 
EXECUTION COPY

December 8, 2010

Flagstone Reinsurance Holdings, S.A.
37 Val St. Andre
L 1128
Luxembourg

Re:  Share and Warrant Purchase Agreement

This Letter Agreement (this “Agreement”) is among Limestone Business Limited, a
limited company organized under the laws of the British Virgin Islands
(“Limestone”), Haverford (Bermuda) Limited, a company organized under the laws
of the Islands of Bermuda (“Haverford”), Mark J. Byrne of Roughill, 6 Long Lane,
Hamilton Parish, Bermuda (“Byrne”), and Flagstone Reinsurance Holdings, S.A., a
company organized under the laws of Luxembourg (“Holdings”).

Reference is made to the Share and Warrant Purchase Agreement dated as of
December 8, 2010 (the “Purchase Agreement”), among Limestone, Haverford, Byrne
and Flagstone (Bermuda) Holdings Limited, a company organized under the laws of
the Islands of Bermuda (the “Company”).  Terms used but not defined herein shall
have the meanings assigned thereto in the Purchase Agreement.

The parties hereto agree, in consideration for the mutual promises contained
herein, and other good and valuable consideration, the receipt and sufficiency
of which is hereby acknowledged, as follows:

1.        Standstill. From the date of this Agreement until the third
anniversary of the Closing Date (the “Restricted Period”), none of Limestone,
Haverford, Byrne will, nor will any of them permit any of their respective
affiliates to, and Byrne will not permit his spouse or children to, in any
manner, directly or indirectly, (a) acquire, offer to acquire, agree to acquire
or make any proposal to acquire, by purchase or otherwise, or become directly or
indirectly the beneficial owner of, any securities, or direct or indirect rights
to acquire any securities, of Holdings or any subsidiary of Holdings or of any
successor to or person in control of Holdings, or any cash settled call options
or other derivative securities or contracts or instruments in any way related to
the price of shares of common stock of Holdings, or any assets or property of
Holdings or any subsidiary of Holdings or of any such successor or controlling
person; (b) make or in any way participate in any “solicitation” of “proxies”
(as such terms are used in the rules of the Securities and Exchange Commission)
to vote, or seek to advise or influence any person with respect to voting of,
any voting securities of Holdings or any of its subsidiaries with respect to any
matter, or call or seek to call a meeting of Holdings’ stockholders or initiate
any stockholder proposal for action by Holdings’ stockholders, or make a request
for a list of Holdings’ shareholders, or seek election to or to place a
representative on the board of directors of Holdings or seek the removal of any
director from the board of directors of Holdings; (c) make any announcement with
respect to, or solicit or submit a proposal for,

 
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or offer of (with or without conditions) any merger, consolidation, business
combination, tender or exchange offer, recapitalization, reorganization,
purchase or license of a material portion of the assets and properties of or
other similar extraordinary transaction involving Holdings or any of its
securities or subsidiaries; (d) form, join or in any way participate in a
“partnership, limited partnership, syndicate or other group” (as defined in
Section 13(d)(3) of the Securities Exchange Act of 1934, as amended (the
“Exchange Act”)) with respect to any securities of Holdings or any of its
subsidiaries or otherwise in connection with any of the foregoing; (e) otherwise
act, alone or in concert with others, to seek to control or influence the
management, board of directors or policies of Holdings or any of its
subsidiaries; (f) take any action that could reasonably be expected to require
Holdings to make a public announcement regarding any of the events described in
this paragraph; (g) request Holdings or any of its subsidiaries, officers,
directors, employees or affiliates, directly or indirectly, to amend or waive
any provision of this paragraph; (h) to contest the validity of this agreement
or seek a release of the restrictions contained herein (whether by legal action
or otherwise); (i) disclose (including without limitation the filing of any
document or report with the Securities and Exchange Commission or any other
governmental agency) any intention, plan or arrangement inconsistent with any of
the foregoing; or (j) have any discussions or negotiations regarding or enter
into any arrangements, understandings or agreements (whether written or oral)
with, or advise, assist, encourage or direct any person to do, or to advise,
assist, encourage or direct, any other person to do, any of the foregoing, or
make any investment in any other person that engages, or offers or proposes to
engage, in any of the foregoing, other than a passive investment below 5% of the
total equity and voting power of such person made without knowledge that such
person engages, or offers or proposes to engage, in any of the
foregoing.  During the Restricted Period, Limestone, Haverford and Byrne shall
promptly advise Holdings of any inquiry or proposal made to any of them, with a
proposed price, with respect to any of the foregoing.  Notwithstanding any of
the foregoing provisions of this Section 1, none of Limestone, Haverford or
Byrne shall be prohibited from acquiring, either directly or indirectly, any
securities of Holdings so long as the aggregate amount of Holdings’ securities
held collectively by Limestone, Haverford, Byrne and his spouse and children,
any of their affiliates and any other member of any “partnership, limited
partnership, syndicate or other group” (as defined in Section 13(d)(3) of the
Exchange Act) to which any of Limestone, Haverford or Byrne belongs, is less
than 5% of the outstanding amount of any class or series of Holdings’ securities
including, if applicable, on an “as converted” basis.

2.        Resignation.  Byrne hereby resigns, effective upon the Closing, as a
member of the Board of Directors of Holdings.

3.        Indemnification; D&O Insurance.  Byrne will continue to be indemnified
for Byrne’s actions taken while an employee or director of Holdings to the same
extent as other former employees and directors of Holdings under the statuts of
Holdings, and Byrne will continue to be covered by the directors’ and officers’
liability insurance policy of Holdings as in effect from time to time to the
same extent as other former employees of Holdings, each subject to the
requirements of the Law of 10 August 1915 on Commercial Companies of the Grand
Duchy of Luxembourg.

 
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4.        Termination.  This Agreement shall automatically terminate upon the
termination of the Purchase Agreement in accordance with its terms.

5.        Consent to Jurisdiction.  Each of Holdings, Byrne, Limestone and
Haverford irrevocably submit to the non-exclusive jurisdiction of the courts of
Bermuda, for the purposes of any suit, action or other proceeding arising out of
this Agreement or any transaction contemplated hereby.

6.        Governing Law.  This Agreement shall in all respects be interpreted,
enforced and governed under the laws of Bermuda without regard to conflicts of
laws principles or choice of law provisions that would cause the application of
the law of any other jurisdiction.  It is the intention of the parties to this
Agreement that the laws of the Bermuda shall govern the validity of this
Agreement, the construction of its terms, the interpretation of the rights and
duties of the parties, and its enforcement.

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IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be duly
executed as of the date first written above.

                                           LIMESTONE BUSINESS LIMITED,
                                           by Solon Director Limited, as its
Director
 
                                           by /s/ Wyn Hugues
     
Name:           Wyn Hugues
 
Title:Authorized Signatory
   
                                                   by /s/ Maria Patterson
 
Name:           Maria Patterson
 
Title:Authorized Signatory

                                           HAVERFORD (BERMUDA) LIMITED,
                                           by /s/ Mark Byrne
     
Name: Mark Byrne
 
Title: Director

         
Mark J. Byrne

Accepted and Agreed:

FLAGSTONE REINSURANCE HOLDINGS, S.A.,
by /s/ William F. Fawcett
     
Name:           William F. Fawcett
 
Title:Corporate Secretary & General Counsel

 
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