Los Angeles, Sep 26 (IANS): Hollywood star Ashton Kutcher is spilling one of the worst-kept secrets in rom-com history. He recently reunited with his 'No Strings Attached' co-star Natalie Portman for a joint Peloton workout for an episode of his series 'Our Future Selves', released September 20.

During their session, the actor admitted that their 2011 rom-com was pretty darn similar to a certain film starring his now-wife Mila Kunis and Justin Timberlake, released the same year, reports eonline.com.

"I think the first time we really started hanging out is when we shot No Strings together," Kutcher said, to which Portman responded: "Who would've thought 20 years later, we'd be on a Peloton together?"

Kutcher then said: "Wait, it's also weird because my wife was shooting basically the same movie, called 'Friends With Benefits'."

Both Ivan Reitman's 'No Strings Attached' and Will Gluck's 'Friends With Benefits' are about a man and a woman who decide to turn their friendship sexual without becoming a romantic couple, realising later that that's more complicated than they thought.

Both films were successful. No Strings Attached made a higher profit domestically $70 million versus $55 million, according to Box Office Mojo.

Curiously, both films earned almost the same amount worldwide, $149 million. Friends With Benefits had a slightly higher budget, $35 million versus $25 million for the other movie.

On Our Future Selves, Kutcher's interview and marathon training series with Peloton, Portman also raised another curious point to her former co-star.

"And Mila and I had just shot Black Swan together. So we were all making out with each other."

Darren Aronofsky's 'Black Swan', a 2010 ballet thriller, was more than twice as successful at the box office than the rom-coms, making more than $329 million worldwide.