On his blog, Frazetta historian and collector DocDave Winiewicz shares a wonderful story about the above artwork. (To see the whole NSFW painting, click the link below).
[In 1994] Alex [Acevedo, owner of the Alexander Gallery in NYC] was quite interested in buying the Tarzan meets La of Opar watercolor. Frank would not sell it because of the pornographic nature of the piece. Tarzan was shown with a huge erection. This made the piece. One of the slave girls was looking down at the erection with obvious lust in her eyes. The Queen was lifting herself off the throne and thrusting her pubic area toward Tarzan. Great Frazetta ribald humor! A masterpiece. Frank put a lot of work into the details.
Alex wanted it. Frank said that he would have to remove the penis. Alex agreed. I was thoroughly despondent sitting there watching this scenario play out before my eyes. "My God, Frank, you can't take out that penis. It will ruin the piece." I said it calmly and quietly while Alex was looking at other potential acquisitions. Frank simply said: "I can draw another one." I've heard this before and it never happened. Alex was willing to pay 45K for the piece.
Frank got out his gouache bottles and a little water. In a few minutes he had scraped off the penis and flawlessly filled-in the open area. He matched every tone perfectly. It was an amazing thing to see. It is impossible to see that anything different was there before.
Frazetta was well-known for changing his paintings, even decades after painting the original. George Lucas has nothing on Frank!