As Catherine enjoys her honeymoon with new husband Prince William after a flawless royal wedding, back home her little sister Pippa has sparked a media storm all of her own.

Kate Middleton's sister Pippa Middleton

The two sisters had long been seen together at parties, the pair strangely interchangeable with their glossy brown hair and figure-hugging dresses.

But at the royal wedding on April 29, it was Pippa who emerged the star for many of the 2 billion viewers worldwide, looking gorgeous as maid of honor in a figure-hugging white Alexander McQueen dress.

Twitter exploded into a frenzy of admiration, and more than 200,000 Facebook users have now joined fan group dedicated to her.

A mock-up video using footage from the wedding showing close-ups of Pippa's behind has been viewed 550,000 times on YouTube, and a US porn mogul meanwhile has offered her $5 million to star in "one explicit scene".

The 27-year-old fuelled the interest at the wedding by flirting with the best man, William's younger brother Prince Harry, sparking huge online debate about whether a second Middleton sister would soon become a royal bride.

Pippa had been a well-known figure on Britain's social circuit for years, and in 2008 she was named the most eligible singleton in society magazine Tatler. But it was not until a fortnight ago that the world caught up.

"It's all about that bridesmaid's dress. She just looked stunning," said Joe Sene, head of editorial UK at the Splash news and picture agency.

"We have had calls for photos of her left, right and center. Publications around the world have been calling us wanting more pictures of her."

Explaining her appeal, said: "Kate's now married and so Pippa is the available Middleton sister, as well as being a slightly sassier version."

While Pippa is not single - she is dating former cricketer Alex Loudon - she is more eligible than her sister, whose entry into domestic bliss was confirmed last week when she was photographed doing the weekly shop.

She also always looks good and smiles for the cameras, often with a glint in her eye that Catherine does not have.

"Pippa's strikingly attractive. She's a bit of a socialite, she's out with the right sort of people and that makes her interesting," said Phil Hall, a former editor of the News of the World and of Hello! magazine.

Pippa initially seemed to enjoy the attention, but was confronted with the ugly side of fame at the weekend when a tabloid newspaper published pictures of her topless on a 2006 family holiday.

The Middleton family acted swiftly, complaining to the Press Complaints Commission, a regulatory body which enforces a voluntary code of conduct agreed by Britain's newspapers.

Other embarrassing photographs have emerged, however, including one of Pippa in a purple bra posing at a party, and another of her wearing nothing but toilet paper wrapped around her like a dress.

The pictures have spoiled an otherwise perfect media operation around William and Catherine - the latter has never put a foot wrong and been careful not to feed the tabloid press who hounded William's late mother, Diana, to her death.

A palace spokeswoman refused to comment on the storm around Pippa, saying: "It's not something we would get involved in. She's a private individual."

The question now is whether Pippa will shy away from her newfound publicity, or use it to her advantage, including by furthering her business interests. Having graduated with a degree in English from Edinburgh University in Scotland, Pippa now works three days a week for Table Talk, an event catering company in London.

The rest of the time she is at the Middleton family party supplies business, where she set up an online newsletter, Party Times. Both businesses would benefit from her new high profile and royal connections.

However, Mark Borkowski, who has handled the publicity for stars including Michael Jackson, warned she must be careful. "Fame can be toxic, and there are more casualties than successes," he said.