The Duke and Duchess of Cambridge were guests of honour at the wedding of two of their closest friends yesterday - but it was Kate's sister Pippa who was the talk of the society event.
Pippa, who was attending her sixth wedding of the year, beamed as she walked into the church with boyfriend Alex Loudon, a former England cricketer turned City banker.
And friends close to the couple have indicated that their romance is so serious that Pippa may well be the next Middleton sibling to walk down the aisle.
The Mail on Sunday has been told that Pippa, who turned 28 this month, has moved many of her belongings into Mr Loudon's West London home and been given a set of keys.
Yesterday, party-planner Pippa, who attended another wedding last weekend without her boyfriend, looked elegant in a pillbox hat and a pretty silk patterned frock by Alexander McQueen. Alex, whom she has been dating for a year and a half, wore traditional tails.
Kate, 29, dazzled in a stunning mid-length raspberry coloured lace dress by Canadian designer Erdem and L.K. Bennett shoes.
The Duchess was accompanied by her friend Louise Aubrey-Fletcher. Prince William had arrived earlier to fulfil his duties as an usher at the wedding of their friends Thomas Sutton and Harriet Colthurst at St Mary and St Nicholas Church in Wilton, Wiltshire.
An onlooker said: "There were some photographers at the entrance and William kept his head down and headed straight into the church. Kate just about managed a smile, but Pippa was beaming and walked very close to Alex.'
Sources close to the couple say Pippa has moved some of her clothes and belongings into Mr Loudon's home near Parsons Green in West London.
Although she has her own flat off the Kings Road, Pippa now spends most of the week at her 31-year-old boyfriend's home.
"They are very much an item and Pip tends to stay at his place on a Wednesday, Thursday and often Friday night,' said a friend. "She has her own place in Chelsea and she splits her time between their houses, but she's spending more time at Alex's these days. She's moved some of her things in and he has given her a set of keys so Pippa comes and goes as she pleases. Alex absolutely dotes on her and they are really very serious.'
The couple were seen enjoying a romantic dinner at Chelsea's Medlar restaurant on Thursday night.
"They love going out locally and were having a quiet dinner and drinking lots of wine,' said a source.
"They do spend a lot of time together but they like to keep their romance under the radar. Alex particularly doesn't like lots of fuss and he finds the interest in their relationship baffling and somewhat bemusing.'
The Duke and Duchess are said to get along well with Mr Loudon, a former Etonian who sat with the Middleton family at the Royal Wedding at Westminster Abbey.
This month he joined Pippa, her family, William and Kate at Italian restaurant Locanda Ottoemezzo for her birthday dinner. "They had a lovely, low-key evening. After a pasta dinner and a birthday cake, they went back to Pippa's house for cocktails,' said a source.
"William, Kate and Pippa's parents adore Alex. They trust him and see him as one of the family. They'd be very happy if he slipped a ring on Pippa's finger.'
There were rumours that Alex intended to propose to Pippa last year, but any plans were put on ice after William announced his engagement to Kate in November.
Despite reports that Pippa and Alex had split after she was photographed with her business partner and close friend George Percy, sources close to Pippa say she and Alex have always been steady.
"Pippa is very much in love with Alex and she may well end up marrying him,' said one of her girlfriends.
- DAILY MAIL