Scarlett Johansson and Sean Penn
Brandon Todd/Splash News Online
06/03/2011 AT 07:00 AM EDT
06/02/2011 AT 08:00 PM EDT
and Sean Penn are no longer dating, a source tells PEOPLE.
Speculation about the pair began after Johansson did not attend the Cannes Film Festival with Penn for his movie The Tree of Life
. She has been working on The Avengers
in New Mexico, reprising her role of Black Widow from Iron Man 2.
Johansson, 26, and Penn, 50, made headlines when they took a whirlwind trip
to Cabo San Lucas after being spotted getting flirty together during a lunch date in Los Angeles.
The pair attended a
White House Correspondents' Dinner party in Washington D.C. in April and had been spotted in a series of cozy outings in L.A.
The reason for the split wasn't immediately known. Reps declined to comment.