Prince William was an usher at the society wedding of his friend Hugh van Cutsem in Oxfordshire on Saturday.
The groom protected his bride from the rain with a white umbrella
Other guests included William's girlfriend Kate Middleton, advertising mogul Maurice Saatchi, and The Ecologist editor Zac Goldsmith.
The Prince of Wales and Duchess of Cornwall were not at Burford Parish Church to watch van Cutsem, 30, wed landowner's daughter Rose Astor, 25.
Other well-known faces included Prince William's old nanny Tiggy Pettifer.
The prince's ex-girlfriend Jessica "Jecca" Craig also attended the one-hour service.
The bride, the youngest daughter of David and Clare Astor, wore an ivory dress with lace sleeves and was escorted through the drizzle by her groom under a white umbrella.
Although the Royal Family and the groom's parents Hugh and Emilie van Cutsem have been friends for years, they did not attend Charles and Camilla's wedding blessing at Windsor Castle in April.
Charles had earlier stayed away from the wedding of the van Cutsems' oldest son Edward to the Duke of Westminster's daughter Lady Tamara Grosvenor, in November 2004, after learning Camilla was to be seated some rows behind him.
Hugh van Cutsem, a farmer, conservationist and pro-hunt campaigner from Hilborough, Norfolk, became one of Charles's closest friends when they were both students at Cambridge more than 30 years ago.