Was Pippa Middleton's bum a fake?

Pippa Middleton became a household name when she stepped out wearing that dress at her sister, Kate Middleton's wedding to Prince William in 2011.

She threatened to steal the show from her big sister in the Sarah Burton for Alexander McQueen gown, that hugged her in all the right places.

RELATED: 'Pippa Middleton: My dress fit too well'

However French royal watcher, Stephane Bern claims The Duchess' younger sister “had a false bottom”.

The Frenchman, a Knight of the Order of Grimaldi in Monaco, has suggested Pippa could have worn bum-boosting undies.

Pippa Middleton. Source: Getty Images

“But of course she had a false bottom”, he claimed on his TV chat show.

“I repeat it — she had a false bottom. You take her away from that and she has normal buttocks. It was an optical illusion.

Pippa Middleton. Source: Getty Images

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“She knew there were a billion people watching. It was the moment to show it.”

However he would not say how he knew.

The 30-year-old spoke out for the first time about the dress earlier this year, saying: “As I have found out, recognition has its upside, its downside, and — you may say — its backside,” she admitted.

The maid of honour admitted she was “glad it fitted” at the time of the wedding, but added: “In retrospect, it fitted a little too well.”