LONDON - The Harry Potter films brought great joy to fans and billions of dollars in box-office receipts for film studio Warner Brothers.

But for one of its key stars, Emma Watson, the pressures of the highly popular fantasy series almost proved too much.

"The fame thing had finally hit home in a big way," said Watson, 31, who played Hermione Granger, during the Harry Potter 20th Anniversary: Return to Hogwarts retrospective that premiered on Jan 1 (Saturday) on HBO Max.

The retrospective featured appearances by the cast and crew of the eight Harry Potter films (2001-2011) based on the popular children's books by British author JK Rowling.

In a conversation with her co-star Rupert Grint, who played her love interest Ron Weasley, Watson is quoted by US entertainment trade magazine Variety as saying that it was during production for the fifth film, Harry Potter And The Order Of The Phoenix (2007), "when things started getting spicy for all of us".

"I think I was scared. I don't know if you ever felt like it got to a tipping point where you were like, 'This is kind of forever now,'" she said.

The Order Of The Phoenix was filmed after the release of 2005's Goblet Of Fire.

Watson's fear was serious enough that the film's director David Yates was warned by the studio that "Emma is not sure she wants to come back to do another Potter."

But she later decided to go on with it, buoyed partly by the support of fans.

"No one had to convince me to see it through. The fans genuinely wanted you to succeed and we all genuinely had everyone's backs. How great is that?" she said.

Elsewhere in the special, Watson discussed her crush on Tom Felton, which she previously said had occurred when she was between 10 and 12.

"I used to come in every day and look for his number on the call sheet. And if his number was on the call sheet, it was an extra exciting day," she said.

"He was three years above me, and so for him, he was like, 'You're like my little sister'. I think really, the truth of it was, Tom was the one that I could often be more vulnerable with."

But Watson added: "Nothing has ever, ever, ever happened romantically with us."

For his part, Felton, 34, who played sometimes-villain Draco Malfoy, spoke warmly of their connection: "I became very protective over her. I've always had a soft spot for her and that continues to the day."