The Irish reality TV judge said that his most shocking moment of the latest series of X Factor came backstage and off-camera in Contostavlos's dressing room.
"Ha. Walking in on Tulisa with no clothes on. I sauntered into her dressing room and she was totally naked," Walsh told the official X Factor site.
"That gave me quite a shock! She looks great though, it has to be said."
Walsh also dished out gossip on Contostavlos's relationship with footballer Danny Simpson, claiming that the N-Dubz star was "in love".
"I can tell - she looks really happy and is letting me get away with murder on the show! I enjoy winding her up by calling her a WAG," he said.
Louis Walsh's hairstyles through the years - pictures:
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