The actors spent Thanksgiving at the Center Pompidou in Paris, looking at the museum's modern art collection and dining at Chez Georges, a restaurant boasting panoramic views from the building's top floor.
Culkin, 33, was spotted kissing his new love interest and dancing with her in the street.
On Nov. 22, the former child star was also spied affectionately greeting the All My Children actress at the French capital's Orly airport – welcoming her with a single red rose in a … plastic water bottle.
Four days later, the couple got cozy at the historic Café de Flore on the Boulevard Saint-Germain.
The pair spent two hours at a table with four friends as they smoked cigarettes and sipped Champagne at the nightspot where famed lovers such as Jean-Paul Sartre and Simone de Beauvoir once rendezvous'd. (More recently, the café has attracted the likes of Blake Lively and Quentin Tarantino.)
"They were very animated and talked together a lot," says an observer. "They kissed at the table and were very comfortable. They have the air of being very much in love."
"She really resembles Mila," says the eyewitness. "You could easily mistake one for the other."
And Culkin, who was married to Guiding Light actress Rachel Miner from 2000 to 2002, has clearly moved on, too.
The actor, who recently lent his voice to the animated series Robot Chicken, is now focused on creating artwork and has been living in New York City and Paris.
His brightly colored paintings of pop culture figures such as Kurt Cobain, Super Mario and a nude Jerry Seinfeld were recently exhibited in Manhattan.
Let's hope his new love makes for an inspiring muse.