London, UK - Emma Watson has admitted she felt "quite overwhelmed" ahead of reuniting with members of the original cast of Harry Potter.

But the actor, who plays bookworm Hermione Granger, said she had been "pleasantly surprised" while reliving moments from her years spent filming.

In a clip released by HBO Max, who produced the special, she said: " Some of us haven't seen each other for years.

"It's just been a joy, an unexpected joy. I really didn't know how it would feel.

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She continues: "I felt quite overwhelmed this morning and I've just been quite pleasantly surprised by just getting to relive it all.

In an earlier clip, she said: "It feels like no time has passed and loads of time has passed."

The special, Return to Hogwarts sees her reunited with Daniel Radcliffe, Rupert Grint, and a host of other famous faces on the 20th anniversary of the release of Harry Potter and the Philosopher's Stone.

Members of the cast join American filmmaker Chris Columbus to discuss the beloved movies and explore their creation.

The highly anticipated Harry Potter reunion special will be released on HBO Max January 1, 2022.