Pippa Middleton Pictures at Holly Branson's Engagement Party

Kate Middleton's younger sister, 27-year-old Pippa, hit the town in London last night to celebrate the engagement of her friends Holly Branson and Fred Andrews at the Kensington Roof Gardens. Holly, who's the daughter of Virgin entrepreneur Richard Branson, has decided to make things official with Fred after five years of dating. Pippa didn't bring her 30-year-old boyfriend Alex Loudon to the bash, though he very well may be her date to the royal wedding taking place just one week from today! Alex and Prince William have known each other since they went to school at Eton, though the former's romance with Pippa has only been going on since before the holidays last year. The next week is bound to be a busy one for Pippa as she preps for her maid of honor duties. She was responsible for organizing Kate's bachelorette, or "hen", party last month and did so with such success that no details of the girls-only event leaked to the press.