"Oh my god, you did, you were so nice!" began Grant, 60, after Barrymore, 45, sparked his memory. "It was during the dark days of my Divine Brown scandal, I was just an idiot. I was a grown-up idiot who got caught by the police."
"I was back in England with 5,000 members of the press around the borders of my farm," Grant continued. "I opened a letter, from you, that was very supportive and nice, and it was very cheering up. And I thought, 'I love Drew Barrymore.'"
"Words of support from an actress I didn't know in Hollywood was lovely, so, you will always have a place in my heart."
Barrymore -- whose reckless behavior as a child star often made headlines -- said Grant's scandal "related to [her] own life."
"I think that whether it's an actor or politician or anything in between, we expect people to be infallible, perfect, never flawed -- and God forbid we do anything in our personal lives that we would like to remain personal but we don't have that privilege at a certain point because the cat gets let out of the bag," she explained. "I just had to reach out to you. I just appreciated you."
The actress told Grant he was "just the most charming human," adding that she "loved getting to know" him when they both starred in the 2007 rom-com "Music and Lyrics."
"It's just one of my very favorite movies and it makes me so happy," Barrymore said, to which Grant replied, "I agree with you, 'cause I love to hate the films I've been in and I do hate some of them, but 'Music and Lyrics,' it's impossible to hate. We're so good in it."
The two went on to recall the time they had a drunken makeout session after they ran into each other at a restaurant.
"One of the moments that I had the most moxie, and I don't think we've ever talked about this, I walked into I think it was the Waverly Inn," in NYC's West Village. "This was years ago. I had a few drinks, I walked in and I ran into you. And instead of saying hello, I grabbed you by the collar and I fully started kissing you."
"Yes, I remember that," Grant replied with a smile, before Barrymore then reenacted the priceless expression she said she saw on Grant's face after she had kissed him.
"You were like, the expression was, 'You've never greeted me that way before,' [but] then you had a second thought and you were like, 'You know, I'm not hating this,'" Barrymore jokingly recalled. "And then we flirted and then it was like, 'OK, bye. See you soon.'"
As for Grant, he described the encounter as "really bizarre."
"I was very drunk as well," he admitted, "and I was with some very nice but not drunk studio executives from L.A., and they were very surprised.
"Someone said, 'Oh, there's Drew Barrymore,'" Grant continued. "I get up to say hi and then we make out for 10 minutes and then I sit down again and we go and talk about the script."
See Barrymore and Grant detail how it all went down in the clip, above!