AceShowbiz - Pamela Anderson is spilling the beans in her upcoming memoir, including a bombshell detail of Jack Nicholson's tryst. In an excerpt of "Love, Pamela" obtained by Variety, the actress reveals she once caught the Oscar-winning actor having a threesome at the Playboy mansion.

The 55-year-old writes that she caught "The Shining" actor with "two beautiful women with him" in a bathroom at the mansion. "They were all giggling and kissing up against the wall, sliding all over each other," she recalls.

But that's not all, as Pamela claims that she made Jack orgasm merely by making eye contact with him. "I walked by to use the mirror, bending over the sink to fix my lip gloss. Trying not to look, but I couldn't help myself and caught his eye in the reflection. I guess that got him to the finish line, because he made a funny noise, smiled and said, 'Thanks, dear,' " she concludes the story.

In the book, Pamela also claims that Tim Allen flashed her during the filming of "Home Improvement" back in April 1991. "He opened his robe and flashed me quickly - completely naked underneath," she writes in her soon-to-be-released memoir. "He said it was only fair, because he had seen me naked. Now we're even." Pamela says she just "laughed uncomfortably" at the shocking sight.

Tim, who was 37 at the time of the alleged incident, was presumably referring to Pamela's modeling for Playboy, which helped turn the budding actress into an internationally known sex symbol.

Tim has since denied Pamela's claim, saying in a statement to Variety, "No, it never happened." The 69-year-old funnyman further insisted that he "would never do such a thing."

"Home Improvement" hits the stores on January 31.