ONTD

Alexander Skarsgård is quite the ladies' man! While promoting his new movie,Battleship, in Tokyo in April, the True Blood star got frisky with his co-star Rihanna, 24.

"They went to a geisha bathhouse," an eyewitness tells Life & Style. "They were drinking, and before you knew it they were in a corner getting hot and heavy."

But they're not exclusive: Alex, 35, has also been linked to Charlize Theron, 36, and he's romancing Italian skydiver Roberta Mancino, 31.

"He and Roberta have been seeing each other for a few months," a friend confirms to Life & Style. "He's been courting her and taking her out to dinner a lot. It's not a serious relationship, but they look forward to hanging out together even more. They really like each other."

Before getting close with these ladies, Alexander dated actress Kate Bosworth, 29, for two years until they ended their relationship last summer.