Actress Drew Barrymore has one rule when it comes to working with her longtime co-star Adam Sandler – and it involves live singing.

Drew Barrymore (Credit: John Nacion/Variety via Getty Images)

Drew Barrymore (Credit: John Nacion/Variety via Getty Images)

Drew Barrymore and Adam Sandler (Credit: Gabe Ginsberg/WireImage)

Drew Barrymore and Adam Sandler (Credit: Gabe Ginsberg/WireImage)

During an appearance on her eponymous talk show, “The Drew Barrymore Show,” the two reflected on their friendship and reacted to throwback photos of them working on “The Wedding Singer” (1998) and “50 First Dates”(2004) together.

“Oh, there’s ‘Forgetful Lucy,’ the night we sang ‘Forgetful Lucy,’ right?” Sandler said when a behind-the-scenes photo flashed on screen.

Barrymore chimed in saying, “The fun story with this is that when Adam sings a song to me in our movie,” Sandler interrupted with, “You don’t let me tell you what it is.”

Adam Sandler and Drew Barrymore during 31st Annual People's Choice Awards - Backstage and Audience at Pasadena Civic Auditorium in Pasadena, CA, United States. (Credit: KMazur/WireImage)

Adam Sandler and Drew Barrymore during 31st Annual People’s Choice Awards – Backstage and Audience at Pasadena Civic Auditorium in Pasadena, CA, United States. (Credit: KMazur/WireImage)

Authenticity appears to be the key to the effortless chemistry Barrymore, 50, and Sandler, 59, share on-screen. In both romantic comedies, the pair portray love interests, with Sandler delivering some of his most memorable serenades to Barrymore’s character.

“I won’t let you play it for me beforehand and we do it for real live on camera,” she explained. “That’s the very first time. So when you see me hearing a song ‘Forgetful Lucy’ or ‘I Wanna Grow Old With You’ in ‘The Wedding Singer,’ that is my natural reaction.”

Drew Barrymore and Adam Sandler attend the premiere of the film 'Blended' (Credit: Target Presse Agentur Gmbh/Getty Images)

Drew Barrymore and Adam Sandler attend the premiere of the film ‘Blended’ (Credit: Target Presse Agentur Gmbh/Getty Images)

The award-winning actors also starred in “Blended” (2014), where their character’s Jim Friedman and Lauren Reynolds fall in love. Ironically, their kids also love reminiscing and watching their on-screen chemistry in “50 First Dates.”

“My daughter and Adam’s daughter were watching it at my house the other night and I was like, ‘Why are you guys watching this? Don’t you get enough of me and your dad?'” Barrymore quipped during a previous episode on her talk show. “And they were just so happy and I was like, ‘Oh, but this is so sweet and wonderful.'”