John Williamson, co-founder of Topanga Canyon's Sandstone Retreat, died on March 24 at the age of 80 according to his wife Barbara Williamson. Williamson's battle with cancer ended at a hospital in Reno, Nev.

Widely considered a leading pioneer of the 1960s sexual revolution, Williamson became known as the "messiah of sex," a nickname which he reportedly did not shy away from.

The Sandstone Retreat was a clothing-optional environment where "free love" was encouraged. As many as 500 people gathered at Sandstone on weekends to be naked, swap spouses, and engage in group sex.

"We actually had open sexuality and nudity, but it was optional. We provided a wonderful, wonderful environment in a natural setting, and that natural setting just sort of gave people permission," Barbara Williamson told the Associated Press Thursday. Williamson and his wife were married for 47 years, each experimenting with other partners from time to time. Their relationship remained strong.

With that in mind, here is a short list of five celebrity couples who have allegedly embraced Williamson's pioneering "free love" lifestyle:

1. Larry King and (wife #7) Shawn Southwick

2. Goldie Hawn and ex-husband Bill Hudson

3. Dolly Parton and husband "Carl"

4. Shirley MacLaine and ex-husband Steve Parker

5. Will Smith and wife Jada Pinkett-Smith