Sean Penn Natalie Portman Dating; Sean Penn Cheati...

Hollywood is abuzz with whispers that 27-year-old actress Natalie Portman is involved in a passionate affair with married Oscar-winner Sean Penn, 48.

The alleged couple, who met when they both sat on the jury at the Cannes Film Festival last May, first sent tongues wagging when they were spied enjoying one another’s company over dinner at Sunset Tower Hotel’s Tower Bar on March 17.

Natalie and Sean were “constantly touching each other” as they dined, Star claims.

“They went to a bank of elevators that only goes to the spa or to private rooms,” an eyewitness tells Star. “They came back about 45 minutes later, and that’s when I saw them making out.”

The restaurant tipster continues, “There’s a door outside of the hotel’s Tower Bar that has a bridge to the terrace, so it’s semi-private…I used that path to get to the restroom, and when I came back, I had to go through some curtains — and that’s when I interrupted Sean and Natalie! When they saw me, they were startled and quickly composed themselves.”

Sean Penn has been married to actress Robin Wright-Penn (”Jenny,” Forrest Gump) for 12 years. The couple reconciled after a brief split last spring.