London: A collection of letters written by late British actress Audrey Hepburn has sold for 11,250 pounds -- more than twice its estimate. The 10 letters were penned between 1951 and 1960 to her mentor and lifelong friend Felix Aylmer. They reveal details of a dramatic decade of the actress' life as she rose from an unknown ballerina to Hollywood fame, the BBC reported. They had been estimated to sell at the Bonhams auction here for up to 4,000 pounds. In one letter, the actress wrote that "with a heavy heart" she had broken off her engagement to socialite James Hanson. "It is all very unhappy-making. I fear I thought it possible to make our combined lives and careers work out," Hepburn wrote. It was followed by joy at finding her future husband, actor Mel Ferrer, whom she married in private in 1954. "We want to keep (the wedding) a dark secret in order to have it without the 'press'," she wrote.