And there's no mistaking him four years later in The Hangover Part III, in theaters Friday.
"The cheeks kinda give it away, right?" his mom, Carrie Holmquist, jokes to PEOPLE. In honor of the third installment (the last of the series, promises director Todd Phillips), we give you a trio of little known, fun facts about the littlest member of the franchise.
1. HE WAS SURROUNDED BY THE LADIES IN VEGAS
Little ladies, that is. In the first movie, the role of Tyler/Carlos was primarily played by Grant, secondarily by his twin sister Avery, along with six other babies – all girls. After some early scheduling trouble, the Holmquist twins signed on for the film. "We started shooting in Vegas and it was the pool scene, which was fun," says Carrie. "They had shot for two days prior to us getting there, so there are a couple clips in that movie where it's not Grant or Avery." Otherwise, it's about "60 percent Grant, 40 percent Avery," says their mom.
2. HE LOVES ZACH GALIFIANAKIS
Cooper and Helms hung out with Grant between takes, but it was his scene partner, Galifianakis, who really stood out to the young actor. "Zach did an amazing job loosening Grant up," says his mom. "He's the type of kid who's very analytical and intelligent. So he kind of walks into a room and takes it all in first so it was really nice to have those personalities warm up to him." Today, "When he sees him in the trailer or in the paper, he'll go, 'Oh, there's Zachy!' He's taken to calling him Zachy," says Carrie. "Grant loves him."
"We got to do a promotional photo shoot and that was an interesting day as well," says Carrie. "We were just lounging at the studio waiting for Grant's turn and there's Bradley on one couch and John Goodman walks by and Ken Jeong and I had a great heart to heart. He's a physician and has twins, too. Just nice, nice people."
3. AND HE REALLY DIGS YODA
In addition to playing soccer and loving his Legos, Grant "has an infatuation with Yoda," says Carrie. "He was interested in finding out how he uses his light saber ... but what Grant really likes about him is that he's wise. It really resonates with him that Yoda tries to reason with people first, the idea of using the force and being a great Jedi. I thought that was so cool, for a four-and-a-half year old to realize that. He's pretty amazing."