Aspen Sends Letter Opposing Endurance Solicitation of Authorizations

Aspen Insurance Holdings Limited (“Aspen” or “Company”)

announced today that it has issued a letter to shareholders in opposition to Endurance Specialty Holdings Ltd. (“Endurance”)

solicitation of authorizations. Aspen's Board of Directors urges shareholders to reject both of Endurance's proposals by promptly signing, dating and returning Aspen's BLUE revocation card and disregarding Endurance's white authorization card. Information on Aspen's response to Endurance's unsolicited offer, including links to press releases, presentations, and other important documents and SEC filings are available on the Internet at http://aspen.shareholderresource.com, or on Aspen's website at http://www.aspen.co. Below is the full text of the letter to Aspen shareholders: July 21, 2014 Dear Aspen Shareholder: ASPEN URGES YOU TO REJECT ENDURANCE'S AUTHORIZATION PROPOSALS Endurance Specialty Holdings Ltd. continues to pursue its inadequate offer for your company, Aspen Insurance Holdings – an offer that has become even weaker as a result of Aspen's strong operating results and increasing book value. Endurance is engaging in wasteful and coercive legal tactics as a desperate attempt to create a false sense of urgency among Aspen shareholders and force through its inadequate proposal. Consider the facts: * Aspen is delivering on a clear plan that is generating strong financial results, including approximately 9% growth in book value per share since the beginning of this year.^i * Endurance's offer – inadequate from the start – has become increasingly deficient as a result of Aspen's strong operating results. Endurance's offer is now approximately 1.1 times Aspen's book value.^ii * Endurance's stock – which makes up 60% of its offer – is a highly unattractive currency given, among other reasons, Endurance's low-quality earnings that have been significantly dependent on reserve releases. * All three of the leading, independent governance advisory firms – Institutional Shareholder Services Inc., Glass, Lewis & Co., LLC and Egan-Jones Proxy Services – recommend that Aspen shareholders REJECT both of Endurance's authorization proposals. DO NOT TO SUBMIT ANY WHITE ENDURANCE AUTHORIZATION CARDS – PLEASE SIGN, DATE AND RETURN THE BLUE REVOCATION CARD TODAY If you have questions or need assistance revoking your authorizations for your shares, please contact our agent Innisfree M&A Incorporated: Shareholders call toll-free: (877) 717-3930; Banks and Brokers call collect: (212) 750-5833. We appreciate your input and support. Sincerely yours, /s/                       /s/   Glyn Jones Chris O'Kane Chairman of the Board of Chief Executive Officer Directors