Sienna Miller had to wear fake breasts in a new film as her own cleavage was too small.

The actress, who recently split from fiancé Rhys Ifans, is starring in the forthcoming 'GI Joe' film but the director felt that her chest was not ample enough.

The 'Factory Girl' star plays The Baroness in the upcoming film adaptation of the US TV series and action figure, but admits she was a little taken aback when director Stephen Sommers told her that she needed to look more curvaceous to properly fill out her costume.

"[I wear a] tight black leather outfit. And much bigger boobs," she told UK talkshow host Jonathan Ross.

"They gave me these things that looked like chicken fillets. The director said: 'I'm gonna be honest, I like girls with big boobs', and I don't have them so we made them bigger.

"At least he's honest. But I was mildly offended".

Sommers made the first two 'Mummy' films, and has lined up a cast including Dennis Quad and Brendan Fraser for the 'GI Joe' film.