Showbiz
The singer was talked into displaying the oddity, on the side of her breast, by contestants and audience members at the Channel 4 show.
It first registered with her when she heard Chandler Bing from Friends speak about his "nubbin".
"I thought, 'I've got one of those,'" she explained. "So I went to the doctor and he said, 'It's a third nipple'. Apparently, one in 10 people have them."
Allen pulled down her top and called on a camera man to zoom in on the dimple.
The clip has become one of the most watched on YouTube with more than 400,000 views.
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