Ryan Dunn

By SARAH OLIVER and KATIE NICHOLL

'Very close': Pippa Middleton last month in the arms of her 30-year-old City broker boyfriend Alex Loudon

It was the day Royal Maid of Honour Pippa Middleton dazzled the world in a dress that left very little to the imagination . . . but it emerged that she may have kept something secret after all.

For it seems that Carole and Michael’s second daughter is engaged in all but name to her City broker boyfriend Alex Loudon.

The couple have stayed silent about the future of their relationship for fear of detracting attention from William and Kate.

Catching Harry's eye: Pippa and the Prince on the Palace balcony. He had already walked arm-in-arm with her down the Abbey aisle

The Duke of Edinburgh and Prince Harry, who flirtatiously walked her arm-in-arm back down the aisle after the wedding ceremony, were two of her most immediate admirers in the Abbey. Outside, her appearance ignited the blogosphere and almost led to the crash of Twitter. In America and Australia too, Pippa was declared a knockout.

Those in the Abbey who watched her arrival thought just one thing – that Pippa looked smoking-hot in what was probably the kind of dress Kate would have chosen if she had been a Bucklebury bride and not marrying into the House of Windsor.

We are amused: Pippa pulls a face as a beaming Harry makes a wisecrack

But the revelation of the day was not just what a wonderful rear view Pippa offers – her bottom now has its own internet appreciation society, which already had 54,000 members last night – it was her polish, her self-possession, her grace and her diligence towards her sister.

Just as the fraternal bonds between William and Harry were plain to see, the Middleton girls seemed to have a powerful, loving link, with Pippa the best supporting actress in her sister’s romantic drama.

Pippa with Alex on Bond Street where tailors Ede and Ravenscroft was closed to the public while he was fitted for his suit for the wedding

Much has been written about Kate, already the subject of several biographies, but what do we know of Pippa? Philippa Charlotte Middleton is Carole and Michael Middleton’s second daughter (she is 27 to Kate’s 29) and their middle child. She was not even at school when her parents founded their company, Party Pieces, on which they would build the family’s financial and social success.

She lived the first ten years of her life in a four-bedroom Victorian villa in Bradfield Southend, Berkshire, before the family moved in 1995 to the mansion where they remain today, two miles away in the village of Bucklebury.

Like her sister, Pippa attended Marlborough College in Wiltshire before following in her footsteps to a Scottish university. But while Kate chose St Andrews, where she met her Prince, Pippa selected the party town of Edinburgh.