Pamela Anderson and Vivienne Westwood at Paris Fashion Week - Vivienne Westwood Ready-to-Wear Autumn/Winter 2009 - Catwalk, Paris, France - 06.03.09

The busty mum of two was rehearsing for a runway show when her left nipple popped out of her top.

Giggling Anderson quickly covered up and carried on modelling the British designer's wares without a hitch.

A catwalk watcher tells WENN, "It was hilarious and Pam didn't didn't seem to mind a bit that everyone had seen more than they were supposed to. I guess when you've bared all for sex tapes and magazines, something like this is nothing."

Source: WENN