Johansson, Penn 'definitely dating'

Scarlett Johansson and Sean Penn are "definitely dating", according to an onlooker who witnessed their latest outing together.

The pair have been spending time with each other in recent weeks, and were rumoured to have taken a trip to Mexico last month.

According to The Mirror, the alleged couple have been spotted dining at Hollywood's Chateau Marmont.

A fellow diner told the newspaper: "They're definitely dating - well, either that or they are conjoined twins."

Johansson announced her divorce from Ryan Reynolds in December after two years of marriage while Penn split from former wife Robin Wright in 2009.

> Johansson 'is head over heels for Penn'