When Kate Middleton stands at the altar of Westminster Abbey April 29, little sister Pippa will be by her side, as she so often is.
"Although she is Kate's younger sister, she has that role of Kate's best friend as well," ABC News' royal contributor Duncan Larcombe said.
But Middleton's maid of honor has a slightly different reputation from her sister. "Pippa has a reputation as being the really fun one, slightly louder and more outgoing than Kate," Tatler magazine editor Catherine Ostler said. "Possibly slightly naughtier."
As one cheeky newspaper headline said: "Sure You Picked the Right Sister Wills?"
"To a certain section of British men, she's become the most eligible girl in England," Ostler said. "At parties, people are always terribly keen on talking to Pippa. And she has a magnetic effect on men."
But she's taken. The youngest Middleton sister is dating a young English gent: a square-jawed, well-heeled pro cricketer turned businessman.
"She's a Chelsea party girl, almost to the extreme," Ostler said.
It is her job, after all. Pippa Middleton, 27, launched The Party Times, an online party magazine.
She has it sorted, she can enjoy the fun and frolics of a princess lifestyle with her sister, 29, but doesn't have to turn up in the morning for royal duties.
"Without saying that she's cashing in on it, I think it's very convenient for her social status that her sister is about to become one of the most famous people on the planet," Larcombe said.
Indeed, Pippa Middleton (short for Philippa) is in the thick of the royal posse. She is often photographed with the young royal set: Princesses Beatrice and Eugenie, and Prince Harry's on-off girlfriend Chelsy Davy.
"There are some real concerns within the palace circles that one of the wider consequences of the wedding is that suddenly Kate Middleton's wider family will start becoming the story," Larcombe said.
After all, Kate Middleton's uncle Gary was stung by a tabloid newspaper, allegedly taking cocaine. He is, however, still invited to the wedding.
But Pippa Middleton is no live wire. She's loyal and discreet; so far the most controversial thing she has done is to be photographed wrapped in toilet paper at a fancy dress party.
What's unclear, however, is whether the queen will bestow a title on her after her sister marries a prince.
"She's a celebrity in her own right now," Tatler magazine's Ostler said. "The rumor is she'll become her lady in waiting."
For now, though, she's a dedicated maid of honor. She's also apparently her big sister's gym buddy, as they both get in shape for the big day.