Daniel Radcliffe Reveals Which 'Harry Potter' Co-Star Left Him Starstruck Back in the Day

He admitted to being too young to be intimidated by most of his famous co-stars at first.

Just like Harry Potter entering the Wizarding World as a boy, Daniel Radcliffe was not impressed by the world of celebrity when he first joined the magical franchise. 

The 32-year-old actor, who famously played the Chosen One, reflected on the 20th anniversary of the first film, Harry Potter and the Sorcerer's Stone, during an appearance on The Late Show With Stephen Colbert on Wednesday. Radcliffe was cast in the movie at age nine and said that though he was surrounded by an award-winning cast of British actors, he wasn't starstruck. 

"Now I'm aware of who they are in a more significant way than I was when I was nine or 10," he said.  

Not even the legendary Maggie Smith, who played Professor McGonagall in the films, impressed him. 

"I met Maggie Smith when I was nine for the first time. I was doing, before Potter, David Copperfield, a BBC adaptation," he explained, noting that Smith was the person to recommend him for Potter. "I didn't know who she was. My parents were like, 'Oh my god, you're working with Maggie Smith, that's huge.'"

But Radcliffe admitted he wasn't quite as impressed when he met her. 

"I met her completely without any fear or embarrassment, as only a 9-year-old can. I knew she was a dame, so I was like, 'Do you want me to call you 'Dame'?' were the first words out of my mouth and she was just immediately charmed," he shared. "And she was like, 'Don't be ridiculous, just call me Maggie.'"

The stage and screen star does admit to eventually getting starstruck by one of his Potter co-stars. 

"At the time, I wasn't starstruck by any of those people. The first person I remember being starstruck by was Gary Oldman because that was the age where I was aware of who he was and his work and also getting more serious about acting myself," he revealed. 

Oldman played Potter's godfather, Sirius Black, in the franchise and was first introduced in the third film, Harry Potter and the Prisoner of Azkaban

Radcliffe opened up about his experience working with Oldman last month while talking to ET

"I have really, really fond memories of all my scenes with Gary Oldman and David Thewlis," he told ET. "They were some of the first scenes on the third and the fifth film where I started to feel like I was a young man who was just starting to figure out what acting was, and they were pretty cool people to be around."