'Harry Potter and the Philosopher's Stone' Turns 15: See What Hogwarts' Most Beloved Students Are Up to Now!

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"You're a wizard, Harry!"

It's hard to believe it's been 15 years since we first heard Robbie Coltrane deliver that line in character as Rubeus Hagrid in Harry Potter and the Philosopher's Stone, the first of what would turn into eight total fantasy films based on the beloved "Harry Potter" book series by J.K. Rowling.

Nov. 16, 2001 marked the day the world was introduced to Daniel Radcliffe as Harry Potter, Emma Watson as Hermione Granger and Rupert Grint as Ron Weasley. Potterheads quickly fell in love with their unbreakable bond on-screen, which was noticeably just as strong when the cameras weren't rolling.

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In celebration of the franchise's 15th anniversary, ET's taking you back in time to the trio's first moments together at the Hogwarts School of Witchcraft and Wizardry, to see just how far these talented stars have come since their Gryffindor days.

WATCH: 'Harry Potter' Stars Reunite for Tour of 'Diagon Alley' Attraction

"I started to cry, I was so happy," Radcliffe told ET about his time on set ahead of the first film's release, while Watson called it "good fun" and Grint gushed it was his "favorite!"

Radcliffe, now 27, was only 11 years old when he walked the red carpet for the world premiere of Harry Potter and The Philosopher's Stone, held at the Odeon Leicester Square cinema in London. The British actor looked dapper in a suit, which he paired with a bright blue button-down shirt and adorable smile.

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"My stomach's vibrating," he joked to a reporter. "So is my face, actually. It's quite scary because it's never happened before."

He appeared just as sweet onscreen, donning his signature Gryffindor scarf and round-framed glasses, a look fans of the franchise still imitate each Halloween and during trips to Universal Studios' Wizarding World of Harry Potter theme park attractions in Florida, California and Japan.

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Watson also had a permanent grin on her face at the world premiere, stepping out in a custom-made dress, furry feather boa and purple alligator boots. On the red carpet, she told reporters that getting dressed up was one of her favorite parts about attending the premiere. "It's great," she said. "I've never seen so many people in my life! It's nerve-wracking."

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The actress, now 26, certainly didn't show any signs of nervousness on-screen, however. Her character was known for being one of the most brilliant and bravest students at Hogwarts. According to IMDB, Watson and her fellow young actors would do their actual schoolwork in the movie to make the school setting more real.

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While Radcliffe and Watson pulled out all the stops with their premiere ensembles, Grint went super casual, layering an olive green jacket over a brown zip-up sweatshirt and T-shirt. He looked equally adorable, nonetheless.

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During a press junket for the film, Grint couldn't stop gushing over the reasons why he fell in love with his character. "I really feel like I can relate to [Ron]," the now 28-year-old actor revealed. "He's really loyal to Harry. He tries to be brave. He's funny. He's got really good lines, some really good stuff."

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And who could possibly forget Harry, Hermione and Ron's former nemesis, Draco Malfoy, portrayed by Tom Felton? The actor, now 29, seemingly took a style cue from Radcliffe for his first-ever premiere, donning a navy suit with a matching dress shirt and tie.

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That too-cute-for-words smirk was much more charming than his evil demeanor on-screen. "Everyone is going to hate me," he joked to reporters on the carpet, while describing his villainous role.

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Fifteen years later, all four stars have achieved massive success.

Radcliffe branched out to stage acting in 2007, starring in New York and London productions of Equus, and Broadway's revival of the musical How to Succeed in Business Without Really Trying in 2011. He also appeared in a number of films, including The Woman in Black (2012), Kill Your Darlings (2013), The Gamechangers (2015), Now You See Me 2 (2016) and most recently, Imperium. His next role is in the Greg McLean-directed drama Jungle, out next year.

Meanwhile, Watson is gearing up for her highly anticipated role as Belle in the live-action re-imagining of one of Disney's most iconic fairy-tales, Beauty and the Beast, which will hit theaters in March 2017. Directed by Bill Condon, the remake features an all-star cast that includes Luke Evans, Kevin Kline, Josh Gad, Ewan McGregor, Stanley Tucci, Gugu Mbatha-Raw, Audra McDonald, Ian McKellen and Emma Thompson.

"So happy I get to show all of you the new teaser poster for Beauty and the Beast!" Watson shared via Facebook earlier this month. "You are the very first people to see this. I hope you like it."

Prior to her casting in the forthcoming adaptation, Watson appeared in a number of films following the final Potter movie, including My Week With Marilyn (2011), The Perks of Being a Wallflower (2012), The Bling Ring (2013), and This Is the End (2013).

WATCH: Daniel Radcliffe on Transition from 'Harry Potter'

Grint, who starred in Into the White (2012), CBGB (2013) and Moonwalkers (2015), has also taken his talents behind the camera. He's executive producing a new Crackle series titled Snatch, an adaptation of the Guy Ritchie movie of the same name. Grint will star in the scripted drama alongside former Gossip Girl star Ed Westwick and The Musketeers' Luke Pasqualino.

Back in July, The CW announced that Felton would be joining the cast of another beloved franchise, The Flash. "It's always very nerve-racking when you're joining such a well-oiled machine," Felton told ET at the time. "But I've only been around them for less than a few days, and I already feel like part of the family."

In addition to his film roles, including Rise of the Planet of the Apes (2011), A United Kingdom (2016), Message From the King (2016), Felton made a few additional appearances on the small screen, in shows like Full Circle, Labyrinth, and Murder in the First.

Although Potterheads around the world certainly miss seeing these young celebrities together on screen, we can't wait to see what they'll do next.

As the great Harry Potter would say, "Working hard is important. But there is something that matters even more. Believing in yourself."

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