Mindful that next week they'll have key roles in one of the biggest celebrations the country has ever seen, the young royal set were careful to keep it low key at the festivities marking the engagement of one of their friends.
Kate Middleton's maid of honour, her younger sister Pippa were among guests invited to celebrate another love match.
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The party on Thursday was for Virgin boss Richard Branson's daughter Holly, who will marry her shipbroker fiancé Fred Andrews on November 20 at the family's luxurious Necker Island retreat - 22 years to the day after her parents tied the knot there themselves.
Also toasting the couple, who were brimming with happiness at the do in a swanky London venue were Princesses Beatrice and Eugenie.
Pretty in a layered peach mini dress that showed off her tanned pins to perfection, Pippa looked remarkably composed as she faced a barrage of cameras outside Kensington Roof Gardens.
And the younger Miss Middleton looked equally fresh-faced and calm on leaving, proving that she's learned lessons from her big sister.
The future Princess was impeccably turned out when she was spotted this week even though it was just for a spot of last-minute honeymoon shopping on the high street.