Rupert Grint has spent nearly half his life as Harry Potter's best friend, Ron Weasley.
"It's been an amazing few years, which started when I was 10 or 11," Grint, 20, said in an interview for ABC News Now's "Popcorn With Peter Travers."
Grint is starring in the sixth and latest Hogwarts film, "Harry Potter and the Half-Blood Prince," which opens Wednesday in theaters throughout the country
The film premiered in London last Tuesday during a torrential downpour, soaking the "Harry Potter" cast, including Grint, who had just recovered from a bout with the swine flu.
"It was just like any other flu," he said. "It started with a sore throat and I stayed in bed for a while. I had to be off for five days but it was nothing to worry about and cleared itself up quickly."
Weasley, Grint said, has changed a lot in the latest installment -- he has a girlfriend for the first time and finally joins the Quidditch team, which plays the fictional sport developed by Rowling.
"The Half-Blood Prince" explores the adolescent struggles of Ron and best friends Harry (Danielle Radcliffe) and Hermione (Emma Watson). Harry ends up dating Ron's sister Ginny (Bonnie Wright), while Hermione pines for Ron, who has a girlfriend but really cares for Hermione.
"Harry Potter" fans have been waiting for a major kissing scene between Ron and Hermione, which completely changes their relationship.
"We filmed it, Grint admitted. "I have known her since I was nine -- we're more like brother and sister, really, so it was kind of weird. The hardest part was pulling back from the kiss and looking at each other like we're in love without laughing."
In short, Grint has had to rely, increasingly, on his acting skills.
"At first, I wasn't concerned about acting -- just reading my lines," Grint said. "But, over the years, I have become more comfortable."
Grint's experience has expanded with the various directors with whom he has worked. In the eight years since the release of the first film, "Harry Potter and the Sorcerer's Stone," the cast has been led by four different directors: Chris Columbus, Alfonso Cuaron, Mike Newell and David Yates.
When Cuaron came on board to direct the third film, "The Prisoner of Azkaban," he "changed everything," Grint said.
"We were scared but he was crazed and gave energy to the set."
There are two films left in the series. Warner Bros. split the last Harry Potter Book, "Harry Potter and the Deathly Hallows," into two movies, which were filmed back-to-back under Yates' deft direction. They will be released in 2010 and 2011.
Grint was a Harry Potter fan before he got the role.
"I always saw myself as Ron when I was reading the books," he said, "and, over the years, we merged into the same person. I have always related to him."
J.K. Rowling, the author of the "Harry Potter" series and the creative genius behind the films, has played a supporting role.
"She comes to the set occasionally and it's exciting to have her on set," Grint said. "She gives good feedback and she gave me "Spinal Tap" on DVD for my birthday, which was very cool."
Grint's fan base has grown exponentially as he has grown older and he has noticed a difference between British and U.S. fans.