Gwyneth Paltrow was left red-faced after realising she bared her butt in a revealing dress at the Iron Man 3 premiere in Los Angeles on Wednesday night (24Apr13), branding her fashion choice "a disaster".

The actress turned heads when she walked the red carpet in a daring Antonio Berardi gown, which featured sheer side panels and left her backside on display, and she has now revealed the outfit was put together in a hurry as she was running late following a Tv show taping.

The 40 year old, who was this week (beg22Apr13) named the world's most beautiful woman by America's People magazine, decided against wearing underwear with the dress, and as a result, she faced a last-minute intimate grooming session.

Speaking to U.S. chat show host Ellen DeGeneres, Paltrow says, "Oh, I kind of had a disaster. I was doing a show and I changed there and I went (sic) I couldn't wear underwear. I don't think I can tell this story on Tv...

"Well, let's just say everyone went scrambling for a razor... So I went from being the most beautiful to the most humiliated. In one day... I work a 70s vibe. You know what I mean?"

The full interview with Paltrow airs in the U.S. on Friday (26Apr13).