Stephen Postlewhite, chief executive officer of Aspen Insurance, is leaving with immediate effect after 15 years with the company.

The Bermudian insurer and reinsurer announced the news a day after it estimated an underwriting loss of $245 million for the fourth quarter of last year, prompting CEO Chris O’Kane to describe Aspen’s 2017 financial performance as “deeply disappointing”.

David Cohen, chief underwriting officer of Aspen Insurance, will lead the day-to-day management of the insurance business, reporting to Mr O’Kane.

Mr O’Kane said Mr Cohen had made positive changes since joining Aspen in November 2015.

“Since his arrival, he has upgraded the underwriting talent in our insurance segment, is refocusing our underwriting book and is positioning Aspen Insurance for success in the next stage of its development,” Mr O’Kane said.

“David is a strong and well-respected leader and I am confident that as we move forward, he will drive improvements across our Insurance business.”

Mr O’Kane also praised Mr Postlewhite’s “significant contribution” to Aspen.