The two have sparked romance rumors since 2013 and have occasionally been seen together in public but have never confirmed a relationship. E! News has learned last year that the notoriously private stars have been dating for years and that that is "not a secret among their friends."
"Jamie wrapped filming on Robin Hood and Katie flew in to Paris to meet him for a few days," a source told E! News exclusively. "Tom Cruise was filming Mission Impossible 6 only a few blocks away, but Katie and Jamie stayed inside their hotel...and didn't leave."
M:I6 began filming in Paris in April.
Stuart Ramson/Invision for Quaker Oats; Brennan Lashever/ABImages via AP Images
Foxx plays Little John in a new Robin Hood film, which is being filmed in Croatia and Hungary and is set for release in 2018.
The source told E! News Foxx and Holmes were scheduled to return to the United States Tuesday via private jet but were told there was a problem with the plane.
"Jamie had a big smile on his face as they returned to their hotel and snuck in through a private entrance," the source said. "They were very discreet and made sure to always enter and exit the hotel and the car separately."
Another source said the two flew out of Paris together on a private jet Thursday morning.
Prior to this week, Holmes and Foxx were most recently spotted together in April, on a dinner date in New York City.
Last year, former Real Housewives of Atlanta star Claudia Jordan appeared to confirmed the pair's relationship on comedian Theo Von and filmmaker-journalist Matt Cole Weiss' Allegedly podcast, saying, "He is very happy with her." She later said she "misspoke,"
"I have no knowledge of Jamie with Katie at all," she said. "I've never seen them together. He's never told me he's dating her."
—Additional reporting by Alli Rosenbloom