The singer took the stage just ahead of her friend and ex, Ben Affleck's, appearance at the star-studded event.
Rocking a sparkling, rose gold jumpsuit by Zuhair Murad, the 51-year-old singer took the stage at SoFi Stadium in Inglewood, California, and spoke to the audience about the importance of helping everyone around the world get access to the coronavirus vaccine. The event took place Sunday, May 1, but was televised on Saturday, May 8.
"How's everybody feeling tonight? Welcome to VAX LIVE: The Concert to Reunite the World," Lopez exclaimed. "Look at all these beautiful people! We're all here in the same room. We've been away from our loved ones for too long, but we're back. And while it's getting better for us, there are people all over the world, especially in Africa, India and the Latin world, who still need our help and our vaccines. That's why we're here tonight."
Lopez then shared a personal pandemic story of her own, telling the crowd that due to the coronavirus, she wasn't able to spend Christmas with her mother, Guadalupe Rodríguez, this past year.
"First time in my whole life. We've been away too long, but she's here with me tonight, and she's vaccinated," Lopez shared. "When I was thinking about what song to sing tonight, I remembered the song she always used to sing to me when I was a baby. So if you would indulge me, I'd love to sing that one tonight ... you guys know this one!"
The singer then invited her mom up onstage, and asked her to sing the lullaby she used to serenade her with when she was a little girl -- which happened to be Neil Diamond's "Sweet Caroline," but with the name Jennifer, instead of Caroline.
"Lets sing it like a lullaby, and let's help her out," Lopez said to the crowd, before telling her mom, "Sing it like you used to sing it to me."
Later, Lopez took the stage again for a performance of her 2016 hit single, "Ain't Your Mama." The singer was flanked by backup dancers for the high-energy number, at one point transitioning into a dance break set to Saweetie's "Pretty B**ch Freestyle."
Sunday's big benefit concert also featured an appearance by Ben Affleck, who took the stage alongside Jimmy Kimmel immediately after Lopez's first number of the night. The friends and former flames were both guests at the star-studded event. An eyewitness told ET that Affleck watched Lopez's first performance of the night backstage with Kimmel.
Lopez and Affleck's appearance at the concert came shortly after ET learned that the pair has been spending time together, as friends, following the singer's split from former fiancé Alex Rodriguez.
On Friday, Page Six reported that 48-year-old Affleck, who was engaged to Lopez in 2002 before their split in 2004, had been spotted multiple times visiting Lopez, getting dropped off at her mansion by a white Escalade SUV that allegedly belongs to the triple-threat star.
A source told ET that Lopez and Affleck "are friends and have a cordial, good relationship."
"They obviously have a romantic history, but at this point they only have a friendship," the source said. "They both admire each other professionally, respect one another and feel comfortable with each other."
Additionally, a second source told ET, "Jennifer and Ben have seen each other a few times since her breakup with Alex. Jen and Ben have remained friends over the years and the two are still just that -- friends."
While Affleck and Lopez's reunion might have fans excited about them potentially rekindling their romance, the "On the Floor" singer has remained friendly with a few of her exes, including Marc Anthony. The two were married from 2004 to 2014 and share 13-year-old twins Max and Emme.
"J.Lo makes it a point to have cordial relationships, especially with Marc, since he is the father of her children," a source previously told ET. "Jennifer and Marc have a friendship and are supportive of each other whether it comes to parenting, personal matters or their careers. They have each other's backs."
Lopez and Rodriguez announced their split after four years of together on April 15 with a joint statement. Following their breakup, they were spotted having dinner together at the Hotel Bel Air in Los Angeles, with a source telling ET that they arrived separately and left separately.
-- Reporting by Desiree Murphy.