Meg Ryan and Billy Crystal reunite for ‘When Harry Met Sally’ Super Bowl ad — with surprise guest Sydney Sweeney

Thirty-six years later, Billy Crystal and Meg Ryan have reunited for a “When Harry Met Sally” sequel — sort of.

The two are starring in a Hellmann’s mayonnaise commercial that will premiere during the Super Bowl and bring Harry and Sally back to Katz’s Deli, where the 1989 movie’s infamous “I’ll have what she’s having” scene was shot.

Delivering that iconic line this time? Sydney Sweeney.

“It smells exactly like it did 36 years ago when we made it,” Crystal, 75, said of the Lower East Side pastrami palace. “It was so much fun to be out there at the same table.”

In the 30-second ad, Ryan’s Sally becomes very enthusiastic about her turkey sandwich after adding a little mayo.

“What’s happening? Oh boy,” Crystal’s Harry character says in the commercial, while Ryan’s excitement escalates — imitating how she demonstrated faking an orgasm in the movie.

It didn’t take much to get back into character, Ryan, 63, told The Post.

“There was nothing weird about it — it didn’t feel like, ‘Woah surreal.’ We had … a whole room of people wanting to be in on the joke. That was really adorable,” she said.

Also adorable? Sweeney, who delivers the punchline first said by movie director Rob Reiner’s real-life mom, Estelle.

“I really had to hand it to [Sweeney]. She is game, and funny. Has terrific ideas. Not intimidated — respectful, silly and adorable. Beautiful. She was just great,” Ryan told The Post of meeting the “Euphoria” star for the first time on set.

“Working with legends like Meg Ryan and Billy Crystal on this nostalgic and hilarious ad was such an honor,” Sweeney said in a statement, calling the movie “a rom-com classic.” 

But Crystal, who lost his home in the Pacific Palisades wildfire earlier this month, admitted other Gen Z viewers might not get Harry’s Casanova ways.

“That [deli] scene is a comment on Harry’s dating style — [Sally is] upset with him … She’s offended and she teaches him a lesson in front of 200 people,” Crystal said. “He’s a complicated guy. He’s a complicated character who finally gets it right at the stroke of midnight.”

Getting back into character also brought back a wave of nostalgia for late co-star Carrie Fisher, who died in 2016 from cardiac arrest at age 60.

“I had a long friendship with Carrie. We were pregnant at the same time,” Ryan said of Fisher, who played Sally’s best friend Marie in the film.

She recalled actually jumping on the phone with Fisher while giving birth to her son Jack Quaid, now 32 and an actor himself.

The two were “talking while I was delivering my son. I said, ‘This is what labor sounds like!’” Ryan told The Post.

And as beloved as “When Harry Met Sally” is to this day, Crystal told The Post he never understood why fans wanted a sequel. 

“We felt, why? They worked so hard for 12 years to get to happily ever after that that’s where they should be,” Crystal, 76, said of the characters. “To me, they’re still together.”