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The Toxic singer - who has been frequently pictured in public without panties on - knows it is "stupid" to go out without underwear but just doesn't feel comfortable in it.

Jewellery designer Tuesday Knight, who has been friends with Britney since 2003, said her decision not to wear underwear was "ridiculous".

"I've told her. I've said, 'You can't walk into a store wearing just a shirt with your underwear off, or get out of cars baring all'. I've told her that no one will take her seriously when she does this.

"Britney knows it's stupid, but says she just doesn't like to wear underwear. She doesn't feel comfortable with it on."

The 25-year-old mother-of-two, who has lost custody of sons Sean Preston, two and one-year-old Jayden James to ex-husband Kevin Federline, can't understand why people think she is a bad role model.

Tuesday added to In Touch Weekly magazine: "Britney has always been a good mother. I want people to know that she's the better parent - not Kevin!

"Britney asked me, 'Doesn't anybody get to see this part of me?' The answer is, no, they don't. People just read about her not wearing underwear.

"I knew Britney when she and Kevin first met. She remade her entire life so it was all about him. She didn't even want to sign a prenup. Since then, I've watched her spiral downward."

Britney was photographed several times earlier this year without underwear, one of several incidents leading to rumours of a meltdown.