Lopez and Maluma also performed their love ballad on 'The Tonight Show Starring Jimmy Fallon.'
During an appearance Friday on The Tonight Show Starring Jimmy Fallon, Lopez opened up about a particular scene that had Maluma and J Lo performing in front of a packed house. But instead of recreating a fake concert on a movie set, Lopez, who is one of the film's producers, had a brilliant idea.
"He was having like two nights at Madison Square Garden and, of course, the producer in me is like, 'We can take advantage of this,'" she explained. "'We have a scene, a big scene in an arena. Why don't we do it at your concert.' And he was like, 'Okay.'"
The "Love Don't Cost a Thing" singer, who plays singer Kat Valdez in the film, said her surprise appearance proved to be exactly what would end up in the film, which also stars Owen Wilson.
"It was amazing," she said. "This scene is in the movie and they just didn't expect me to come out at his concert. I've never been out at one of his concerts, and the crowd went wild and we got it all on film and we sang together."
Lopez, who looked stunning in a red dress for the interview portion of her appearance, also touched on what it meant producing the album -- with the Colombian superstar who plays her love interest, Bastian -- specifically for the film.
"This was actually the first time since I did the movie Selena. I didn't sing in the movie Selena, that was [Selena Quintanilla's] voice," Lopez said. "So this is the first time I got to, like, sing, make an album for a film. This is like joining my two worlds together."
And, for the record, the soundtrack to the rom-com stands on its own.
"It's not like a Jennifer Lopez album or even a Maluma album," Lopez explained. "It's a Kat and Bastian album. These are songs that I really picked for the characters and that really, kind of, furthered along the story, just like any good musical. And it really tells the love story. The journey of, you know, finding your true love."
Lopez, whose relationship with Ben Affleck is constantly under the microscope, said the character she played in the film was relatable.
"I also got to play a character who was, you know, a lot like myself, you know, she's in the spotlight. Personal life, public life, trying to make it all work," she said. "Failing miserably at times. But it's a really, really great kind of look behind the behind-the-scenes."
Following her interview, Lopez changed her wardrobe and appeared in a revealing white ensemble to perform "Marry Me." Maluma, the GRAMMY-nominated superstar, stepped out in a chic, pastel suit as the singers exuded undeniable chemistry while performing the love ballad.
"Marry Me" hits theaters on Valentine's Day.