The dance graduate, 25, who often dresses down in jeans (and with scrunchies in her hair), stepped out with the princes' cousins, Princesses Beatrice and Eugenie, to the socialite hangout Annabel's on Thursday night – dressed to the nines in a stunning midnight blue evening gown.
In Kate and William's case, they were reunited after a breakup of about nine weeks. In Harry and Cressida's case, it still remains to be seen.
The couple had been together for two years before splitting last month. Sources tell PEOPLE that their relationship has run its course.
Harry, meanwhile, spent last weekend at a bachelor party in Devon – even joking with a landlady of a pub that he would like to buy it – and playing polo alongside William.
Since then, he sent his first Tweet, on behalf of the Invictus Games. He was in Estonia Friday to meet the troops who helped with the peacekeeping effort in Afghanistan – thanking them "for the tremendous kindness and support you have shown the United Kingdom for many years" – and the weekend will take him to Italy.