John Travolta and Robert De Niro vacation together

Robert De Niro, John Travolta and family enjoy a day in the sun at Skiathos Island, Greece. (Splash News)

It looks like new co-stars John Travolta and Robert De Niro have become fast friends.

The Hollywood heavyweights, who are currently starring together in an action movie called "The Killing Season," have been photographed vacationing together this summer.

Kelly Preston, Travolta's wife, was most recently snapped aboard a yacht owned by Australian businessman James Packer. Meanwhile, De Niro was photographed driving a sea-doo nearby.

See also: Natalie Portman weds in Big Sur, Calif. -- see her wedding dress

De Niro and his wife, Grace Hightower, were photographed last month with the Travolta family on the Greek island of Skiathos. According to E! Online, the families had been traveling separately in Greece (Travolta and Preston vacationed alone together in Mykonos in early July) but united for the day.

But it hasn't been all fun in the sun for Travolta. This week the 58-year-old actor denied assaulting an attendant aboard a Royal Caribbean cruise ship in 2009 after the attendant, Fabian Zanzi, filed a lawsuit in June.

See also: Sylvester Stallone and family mend broken heart over son Sage's death with vacation in France

"This is another ludicrous lawsuit with inane claims," Travolta's lawyer said. "It is obvious that Mr. Zanzi and his lawyers are looking for their 15 minutes of fame."

Travolta and his wife have been putting on brave faces amid claims that the "Pulp Fiction" star has engaged in sexual activity with three different masseuses.