Those adorable kids who grew up making the Harry Potter movies are all grown up, and Rupert Grint (Ron Weasley) is even a dad. The gang's back together in a new reunion special, Harry Potter 20th Anniversary: Return to Hogwarts, streaming now on HBO Max. It's a family-friendly trip down memory lane and you don't even have to be a huge Potterhead to enjoy it. And even the biggest fans likely will learn some new facts about the blockbuster saga.

The special reunites most of the major cast members to reminisce and hug and laugh about the decade they spent working on the films. Author J.K. Rowling is shown only briefly and in archival footage.

Here are the six most interesting surprises from the nearly two-hour show.

1. Hermione had a crush on Draco

Actor Emma Watson, who played Hermione, admits in the special she had a crush on Tom Felton, who played the Potter gang's nemesis, Draco Malfoy. She "just fell in love with him" when he was asked to draw God in an on-set tutoring class, and Felton drew a girl wearing a backward cap on a skateboard. 

From then on, "I used to come in every day and look for his number on the call sheet," Watson said. "It was number seven, and if his name was on the call sheet, it was an extra exciting day."

Felton learned of her crush, but he was three years older than Watson, and nothing romantic ever developed.

2. When Harry met David

Chris Columbus, who directed the first two Potter films, couldn't find anyone to play Harry Potter until he watched a BBC miniseries of Charles Dickens' David Copperfield. The young actor playing David was 10-year-old Daniel Radcliffe in his acting debut. 

It wasn't an easy road to hire him, though, as his parents didn't want young Dan to commit to a seven-film series, especially since at the time it was thought the films would be made in America. But as we all know, Radcliffe signed on, and the rest is magical history.

"I was a really happy kid who had a really haunted quality," Radcliffe says with a laugh.

3. Fire alarm at Hogwarts

There's a beautiful scene in 2005's Harry Potter and the Goblet of Fire where the other magical schools arrive to compete in the Triwizard Tournament held at Hogwarts. Hundreds of lit candles hang magically in the air. But in the special, Radcliffe reveals those were real candles -- or at least some were -- and they began burning through their ropes and falling.

4. Quidditch unmasked

Credit to the various Potter directors -- the scenes of Harry and pals zooming around on brooms playing Quidditch are pretty amazing, and fun to watch. Viewers of the special get a treat -- you'll see behind-the-scenes footage of Radcliffe sitting on his broom, which is just part of a complex prop, with a green screen behind it.

"The hardest scene to shoot was Quidditch," director Chris Columbus admits.

5. Draco and his dad

Jason Isaacs didn't want to play Draco Malfoy's dad, Lucius -- instead he auditioned for the role of Gilderoy Lockhart. Asked to read Lucius Malfoy's lines instead, he was irritated, so read them "through gritted teeth and deeply bitter," Isaacs says with a laugh in the special. Perhaps that helped him get the role.

And Isaacs said that while he loved young Tom Felton, who plays his son, Draco, he was "as unpleasant as could be" to him on set, trying to set up the cruelty that ruled the Draco-Lucius relationship. Once though, he accidentally went too far, smacking Felton's hand with a cane and not realizing the cane had sharp teeth that cut Felton's hand. (The scene was deleted from the movie, but can be watched as an extra feature.)

"It's all right, it's good for the scene," said a teary-eyed Felton, showing that true actor's grit.

6. Order of the not-so-fake phoenix

This last tidbit sounds like an urban legend, but the actors and crew claim it's true. In 2002's Harry Potter and the Chamber of Secrets, which featured Richard Harris playing Dumbledore, we meet Dumbledore's pet phoenix, Fawkes. An elaborate prop bird was created for Fawkes, but Harris reportedly thought it was a real bird.

"So the prop people kept moving it and responding," director Chris Columbus recalls with a laugh, as clips are shown of Harris marveling over the responsive creature. He doesn't say if Harris ever figured out that Fawkes was not an actual living, breathing bird, but just an elaborate puppet.

Tune in to Harry Potter 20th Anniversary: Return to Hogwarts on HBO Max.