Poppy Delevingne, the sister of model and actress Cara Delevingne, is said to be dating Sienna Miller's ex. It has been reported that the 38-year-old has enjoyed a number of romantic dates with Archie Keswick who has been described as "the most eligible bachelor you've never heard of".The 42-year-old Archie is a member of the Jardine Matheson dynasty which owns the Mandarin Oriental Hotel Group.