After enjoying a low-key getaway in the city of love earlier this month, Katie Holmes and Jamie Foxx were spotted boarding a private

jet out of Paris.

The two have been the subject of romance rumors since 2013, and although they’ve never officially confirmed a relationship, multiple sources have told PEOPLE the pair has been casually spending time together for years.

While in Paris, Holmes, 38, met up at a hotel with Foxx, 49, who had been in town to shoot his new Robin Hood movie. A source tells PEOPLE Foxx attended a farewell dinner for the Leonardo DiCaprio-produced film set for release in 2018.

Though Holmes kept a low profile during the trip, she was seen on a sandwich run and at one point had her driver stop at the San Francisco bookstore in St. Germain to pick up a few titles, including Ernest Hemingway’s Old Man and The Sea and A Farewell to Arms, according to a source.