Matt Damon revealed why kissing Scarlett Johansson was "hell" one time while they were filming their 2011 family comedy "We Bought A Zoo."

The 52-year-old actor and his "Opppenheimer" co-star Emily Blunt were discussing proper etiquette for shooting kissing scenes with co-stars in a recent video for LADBible. The two strongly agreed that tooth-brushing, using mouthwash and chewing gum was mandatory though Damon noted that he could "forgive some halitosis." 

During their conversation, the "Good Will Hunting" star recalled a less than pleasant onscreen smooch that he once shared Johansson, 38.

"I had to kiss Scarlett Johansson — can you imagine how horrible that was for me?" Damon joked.

scarlett johansson matt damon at we bought a zoo premiere

Matt Damon recalled kissing Scarlett Johansson on the set of their movie "We Bought a Zoo" after she ate an onion sandwich. (Jim Spellman/WireImage)

"Can you imagine how awful that was?" Blunt quipped. "It's such a shame she has such terrible lips and everything. It must have been so awful."

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"It was hell!" the "Saving Private Ryan" actor said with a laugh.

He continued, "What happened was, we did a shot before lunch, and it was this nice little two-shot that ended in the kiss. And it was really good."

"We went to lunch, and she and I both thought it was over, and she ate like an onion sandwich for lunch," Damon remembered.

Matt Damon and his wife at the Venice Film Festival in 2021

The Oscar-winner has been married to wife Luciana Barroso since 2005. (John Phillips/Getty Images for 20th Century Studios)

The two later returned to the set only to discover that they had to resume filming the kissing scene. 

"She came in, and [director] Cameron Crowe had set the camera up, and it was like a tight shot of the kiss," the Massachusetts native recalled. "And she goes ‘Aw s---!  She goes, ’I literally just had, I had like an onion sandwich. I thought we did this.''"

"The Devil Wears Prada" star jokingly asked Damon if he was "still sort of slightly aroused" by kissing Johansson despite her bad breath.

"No, I was making fun of her that entire time about her onion breath, which I didn't even smell," Damon said.

"Her breath smells like roses," Damon insisted as the pair burst into laughter.

scarlett johnasson colin jost red carpet

Johansson married "Saturday Night Live" star Colin Jost in 2020. (Axelle/Bauer-Griffin/FilmMagic)

Damon and wife Luciana Barroso tied the knot in 2005 and are parents to daughters Isabella, 16, Gia, 14, and Stella, 12. The Oscar winner is also stepfather to Barroso's daughter Alexia, 24, from a previous relationship.

Scarlett shares daughter Rose Dorothy, 8, with her ex-husband Romain Dauriac and son Cosmo, 1, with husband Colin Jost, 40. Johansson and Dauriac were married from 2014 to 2017. The "Asteroid City" actress wed "Saturday Night Live" star Jost in 2020. 

"We Bought A Zoo" was loosely based on Benjamin Mee's 2008 novel of the same name.  In the movie, Damon played a widower and father named Benjamin who realizes that his family needs a fresh start after the recent loss of his wife and his two children's mother. 

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He decides to quit his job and move with his family, but upon finding the perfect house, he learns that he must also purchase a dilapidated and closed-down zoo on the property. As Benjamin works with longtime zookeeper Kelly (Johansson) to renovate and reopen the zoo, he finds himself falling in love with her.

emily blunt matt damon

Damon and Blunt starred in Christopher Nolan's historical drama "Oppenheimer," which premiered last weekend. (Fox News Digital)

The film also starred Thomas Haden Church, Maggie Elizabeth Jones, Colin Ford, Elle Fanning, Patrick Fugit and John Michael Higgins.

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Meanwhile, "Oppenheimer" premiered last weekend and soared past expectations with an $80 million opening at the box office. The historical drama placed second behind the "Barbie" movie, which raked in $155 million in ticket sales and became the biggest debut of the year.

Directed by Christopher Nolan, "Oppenheimer" features a star-studded cast that includes Damon, Blunt, Cillian Murphy, Robert Downey Jr., Florence Pugh, Josh Hartnett, Casey Affleck, Rami Malek, Gary Oldman and Kenneth Branagh.