"I describe it as the luckiest day of my life," he told host Ellen DeGeneres.
Rodriguez said he was looking for his car after having lunch when Lopez tapped him on the shoulder.
"I turn around and I do not recognize this person," the star recounted. "And it's Jennifer, but she's dressed up as Harlee from Shades of Blue and she's in her jeans and her big boots. And it took me about four or five seconds."
"She said, 'It's Jennifer.' I go, 'Oh my God, Jennifer, you look beautiful.' I was so embarrassed and then I got a little nervous," he said. "She says, 'You have my number, reach out.' And I went home that night and reached out."
Lopez had said during an episode of the show in April 2017 that she saw Rodriguez at the restaurant and approached him outside.
"I was having lunch somewhere and he passed by," the singer recalled. "I saw him walk by, and then afterwards, I went outside. For some reason, I just felt like tapping him on the shoulder and saying hi."
Rodriguez and Lopez confirmed their relationship in March 2017. The couple purchased a $15 million apartment together in New York in March following speculation they plan to marry.
"I do believe in marriage," Lopez said in the April issue of Harper's Bazaar. "And I would love to grow old with somebody in a committed relationship. But I'm not forcing anything right now. It's good, it's healthy; we communicate well."