Sean Penn Rivals Robert Pattinson For Natalie Portman's Affections?

It seems Robert Pattinson may have to step up his game against major Hollywood player Sean Penn, if he is to win over Natalie Portman.

The Milk star - who was also recently romantically linked to Lindsay Lohan - was supposedly seen locking lips with Natalie after a private dinner at the Sunset Tower Hotel's Tower Bar on March 17.

"They went to a bank of elevators that only goes to the spa or to private room," a source tells Star magazine.

"They came back about 45 minutes later, and that's when I saw them making out."

The source 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."

Last month Natalie was rumoured to have taken a shine to the Twilight hottie after the pair were seen getting cosy at the Vanity Fair Oscars party in Hollywood.

Sean or Rob? We know which one we'd prefer....

See 20 hot male stars rivalling Rob for the title of Hollywood heartthrob below