KISS star Gene Simmons has been left fuming after a video allegedly showing him having sex with a model was posted on the Internet.

The rocker, who has been dating long-term partner Shannon Tweed for over 20 years, is alleged to have made the tape while carrying out promotional duties as a spokesman for Frank’s Energy Drink.

The video showing a man who appears to be Simmons has been posted on website AVN.com, which is selling the recording to those who wish to download the footage.

According to the site, the woman in the film is not Simmons’ girlfriend Tweed, with whom he has two children, naming her only as a model called Elsa who is reported to work for the drinks company the star was hired to promote.

Simmons and Tweed have been a couple since 1985 and are parents to son Nicholas, 19, and daughter Sophie, 15.