The pair split in March after being engaged for two years.
As the 30-year-old singer closed out her last, sold-out Bichota Tour show in Puerto Rico this weekend, she was surprised on stage by her ex-fiancé and frequent collaborator. The crowd went wild as Anuel, 29, made an appearance and joined her to perform their hit songs, "Culpables" and "Secreto." This marked the first time the two performed together since ending their engagement and their 2019 Culpables Tour.
Karol and Anuel split in March after being engaged for two years.
On Monday, Karol took to Instagram to post photos of the two together while backstage, along with a sweet message to her ex.
"I don't have words to describe this moment," she wrote in Spanish. "100,000 thoughts passed through my head about what was, what we lived together and how things transpired. We had a lot of happy years together and although that stage in our lives is over, the loyalty and gratitude remains."
"You are a brilliant person. I will always admire you," she added. "GRACIAS por hacer mi noche de ayer mucho más especial @anuel."
Karol and Anuel first met in August 2018 on the set of the music video for their song "Culpables." They confirmed their relationship months later, in January 2019, and announced their engagement that April.
"There are no words to explain," Anuel told ET of his happiness on the red carpet at the 2019 Billboard Latin Music Awards, where they made their debut as an engaged couple.
News of Anuel and Karol's split came in mid-March, but the couple took to their social media to confirm and address their breakup in late April.
“If just accepting it is hard enough, imagine having to do it in front of millions of people,” Karol wrote in Spanish on her Instagram Story at the time. "For a long time we tried to keep our relationship away from social media in order to protect ourselves. We never used our relationship for marketing purposes, not today, not even almost three years ago when we started [dating]."
Back in August, Anuel released "23 Preguntas," a song that seemingly alluded to his painful breakup. The song dropped on what would have been his anniversary with Karol.
In the slow-tempo track, the artist asks his ex-fiancee 23 emotionally painful questions -- hence the title of the song -- about their relationship and eventual split.
For more on Karol and Anuel, see below.