The two stars were in Greece making the acclaimed movie about motherhood when they bonded over booze.
In one scene their characters have a drinking session but Oscar-winning Colman said it was not real alcohol.
“No, we weren’t drunk – we weren’t allowed real wine,” said The Crown star.
“But we did get drunk most evenings anyway.”
And Normal People star Mescal confirmed they did have a few jars in the evenings after work.
“Yes. That’s a hard yes,” he told Hits Radio.
“Olivia had this balcony that was the go-to place after filming. It was stunning. And also just fun.
“My balcony kind of connected by a roof and I was able to climb across rather than go [along the corridor].
“I would climb on to her balcony and normally I would find three, four, five or six people there.
“That was the place to go after a day’s filming. She’s the best host. Yes, categorically.”
The Lost Daughter has just earned three-time winner Colman another Golden Globe nomination for Best actress along with an award nod to first time director Maggie Gyllenhaal.
The Favourite star plays Leda, a woman relaxing on holiday on a Greek island who begins to re-examine her role as a mother after becoming obsessed with another family on the beach.
Co Kildare heartthrob Mescal plays Will, a lifeguard who also runs the beach café and who might have a sinister motive for befriending Leda.
Talking of his co-star, Mescal said earlier this year: “What’s not to admire about Olivia Colman?
“She’s just the best. She’s a fantastic leader of the film, she’s amazing fun, she’s so good.
“She’s so brilliant and she’s really generous and she really sets the tone in the film and kind of just by her brilliance she demands us all to get up to her level or you’ll be just wiped off the screen.”
The 25-year-old star, who earned a BAFTA for his poignant role as troubled Connell Waldron in the worldwide hit Normal People, said he was stunned when Gyllenhaal asked him to be in the film with A-listers Colman, Dakota Johnson and fellow Irish star Jessie Buckley, who plays the young Leda in flashbacks.
“It’s pretty special isn’t it? It’s not a bad place to start,” he said at the time.
“That was definitely one of those big moments in my life. When you’re called up and you’re like, ‘Maggie Gyllenhaal wants to have you in a film and you’re gonna be shooting it in Greece and Jessie’s gonna be in it, and Olivia’s gonna be in it, and Dakota’s gonna be in it.’
“It definitely kind of feels like a bit of a ‘fake it ’til you make it’ kind of a thing.
“And working with Maggie was a dream, she’s an actor’s dream. She pushes you and pulls you in directions and it never felt like we were arriving into a scene with a kind of finished product in mind.”
Mescal’s next project is filming Foe with Saoirse Ronan in Australia in January in which they play a couple in the future.
Based on Iain Reid’s bestselling novel, the film is described as “a taut, sensual, psychological mind-bender set in the near future where corporate power and environmental decay are ravaging the planet.”
Junior (Mescal) and Hen (Ronan) are a young couple married seven years and living a solitary life on their isolated farm until a stranger arrives and throws their lives into turmoil.