Aspen Issues Third Letter to Holders: Suggesting Rejection of Both of Endurance's Bids

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

announced today that it is mailing a letter and a BLUE revocation card 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. Earlier today, Aspen announced preliminary financial results for the quarter ended June 30, 2014, which demonstrate the continued benefits of the Company's strategic investments in its business and the strength of Aspen's plan to drive shareholder value. Aspen will report final results for the quarter on July 23, 2014. 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 10, 2014 Dear Aspen Shareholder: ASPEN'S PLAN IS DELIVERING STRONG, HIGH-QUALITY RESULTS Board Urges Shareholders NOT to Submit Any White Endurance Authorization Cards – Please Sign, Date and Return the BLUE Revocation Card Instead As you may have seen, this afternoon your company, Aspen Insurance Holdings Limited, reported strong preliminary financial results for the second quarter, including:   Preliminary Q2 2014 Diluted Book Value Per Share^i       $44.60 – $44.80 Annualized Operating Return on Equity^ii       12.0% – 12.8% Diluted Operating Earnings Per Share^ii       $1.30 – $1.35 Preliminary book value per share figures indicate 4.4%-4.9% growth since March 31, 2014 and 9.0%-9.5% growth since December 31, 2013. Our continued strong performance during the second quarter – following an excellent first quarter – clearly demonstrates the continued benefits of the strategic investments we have made in our business and the strength of our plan to drive shareholder value. Aspen will report final results for the quarter on July 23rd. While we are delivering strong results for shareholders, Endurance continues to pursue its ill-conceived and inadequate offer along with proposals related to the calling of a special meeting and a convoluted legal strategy Endurance has said it will pursue with the Bermuda Supreme Court. These proposals are desperate legal tactics designed to coerce you into selling your shares at the lowest possible price. Aspen strongly urges shareholders not to sign any white authorization cards sent to you by Endurance. Whether or not you have previously executed Endurance's white authorization card, you may reject Endurance's proposals if you sign, date and return the enclosed BLUE revocation card.          ENDURANCE'S OFFER IS HIGHLY INADEQUATE AND IS BECOMING EVEN LESS ATTRACTIVE IN LIGHT OF ASPEN'S CONTINUED STRONG, HIGH-QUALITY RESULTS Our plan is working – we are delivering high-quality results, including diversified revenues and continued strong returns from our investments in our business, and we remain well-positioned to deliver increased value to our shareholders. As our book value grows, Endurance's offer is increasingly inadequate; it now represents about half of the premium to Aspen's book value per share in Endurance's initial proposal. ^ iii ENDURANCE CONTINUES TO MISCHARACTERIZE ASPEN'S CLEARLY SUPERIOR UNDERWRITING RESULTS Aspen's underwriting results have been consistently better than those of Endurance as shown by historic accident year combined ratios in the graph below. Lower ratios represent stronger performance – and Aspen has performed better than Endurance in four of the past five years with continued outperformance in the first quarter of 2014. Aspen's superior results came in spite of the fact that during this period we were investing $150 million in our insurance platform to build underwriting, claims, actuarial, technological and other infrastructure capabilities in the U.S. – investments that are now paying dividends and enabling us to generate even stronger results. In addition, Endurance's results have reflected an increasing reliance on prior year reserve releases, masking the underperformance of its business and raising serious questions about the quality of its earnings. In 2012, Endurance's reserve releases improved its combined ratio by 6 percentage points. This increased to 11 percentage points in 2013 and almost 13 points in the first quarter of 2014. SETTING THE RECORD STRAIGHT ON ENDURANCE'S LATEST ERRONEOUS CLAIMS In a letter filed publicly this morning, Endurance made a number of erroneous and ill-informed claims about Aspen's business, which underscores our deep concern about their failure to understand the significant dis-synergies that would result from the misguided transaction they are proposing. We want to set the record straight: Aspen's catastrophe reinsurance exposures: In contrast to Endurance, Aspen Re has a very strong and successful brand and track record in the catastrophe reinsurance business. Unlike Endurance, Aspen has embraced the significant changes heralded by third party capital in catastrophe reinsurance and views this as a significant opportunity for future growth and diversity of earnings. Since Aspen Re enjoys numerous long-term and highly profitable relationships with core clients, Aspen Re was able to increase its share on some of the most desirable risks in the catastrophe reinsurance market, not only during the important January 1 renewal period, but throughout this year. We have benefited significantly from Aspen Capital Markets, our third-party capital markets entity, which enables us to increase our gross premiums written while maintaining the same net risk position by redistributing risk to the capital markets and at the same time adding underwriting fees and profit commission. U.S. programs: Similar to most major insurers, we have found that for certain categories of smaller and homogenous risks, it is economically beneficial to participate on a program basis, with tight and careful controls over underwriting, claims, and risk management. Currently our U.S. Program business is profitable and represents approximately 6% of our 2013 annual written premium. Reserving: We have consistently said publicly that we aim to maintain our reserves at a prudent level such that the probability of reserve redundancies in future periods is in the mid-to-high 80% range. At year end 2013 the figure was 86%. Endurance references our year end 2011 reserving at the 90th percentile in a veiled attempt to discredit our robust reserving process. The higher than normal percentile selected at that time was due to the extreme catastrophe events that occurred during that year. At year end 2009 our reserving percentile stood at 86%. Furthermore, since Endurance does not make a similar type of disclosure, it is impossible for shareholders to assess the consistency of their reserving strength over time or the relative level of the reserving risk they are taking. This is one of many reasons for our deep concern with receiving Endurance shares in exchange for Aspen's. PROTECT THE VALUE OF YOUR INVESTMENT: PLEASE SIGN, DATE AND RETURN THE ENCLOSED BLUE REVOCATION CARD TODAY Aspen strongly urges shareholders not to sign any white authorization cards sent to you by Endurance. Whether or not you have previously executed Endurance's white authorization card, you may reject Endurance's proposals if you sign, date and return the enclosed BLUE revocation card using the pre-paid envelope provided.  1. Do NOT sign Endurance's white authorization card.  2. Sign, date and return the enclosed BLUE revocation card.  3. Even if you have already signed Endurance's white authorization card, you have every right to revoke your authorizations by signing, dating and returning the enclosed BLUE revocation card. 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. Regardless of the number of ordinary shares of Aspen that you own, your views and your vote are important. Sincerely yours, /s/           /s/   Glyn Jones Chris O'Kane Chairman of the Board of Directors Chief Executive Officer