'Harry Potter' reunion special reveals Daniel Radcliffe's crush on Helena Bonham Carter

The upcoming Harry Potter 20th anniversary TV special reunites the films' actors to look back on the series and is set to give away a few behind-the-scenes cast secrets – including Daniel Radcliffe’s crush on co-star Helena Bonham Carter.

The pair played adversaries in the films with Radcliffe, 32, as the eponymous hero and Bonham Carter, 55, starring as Voldemort fanatic Bellatrix Lestrange.

However, that didn’t stop Radcliffe falling for his castmate, who is 23 years his senior.

Watch: Emma Watson admits feeling 'overwhelmed' ahead of Harry Potter reunion

In the special, Radcliffe reads aloud a note confessing his admiration that he sent to Bonham Carter after filming wrapped on the franchise in 2011.

He says: “Dear HBC, it was a pleasure being your co-star and coaster in the fact I always ended up holding your coffee.

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“I do love you and I wish I’d just been born ten years earlier so I might’ve been in with a chance.”

Other on-set crushes are also explored in the reunion as Hermione Granger actor Emma Watson recalls an infatuation with Draco Malfoy star Tom Felton.

However, their age difference of three years put a spanner in the works for her as she explains: “He was three years above me and so for him he was like, 'you're like my little sister'".

The Harry Potter 20th Anniversary: Return to Hogwarts special celebrates 20 years since Harry Potter and the Philosopher’s Stone hit cinemas, reuniting the cast and directors to reflect on being part of such a huge global hit.

Early reports on the reunion suggested author JK Rowling had been omitted due to controversy surrounding her views on transgender rights, however, first looks at the special have revealed she will be present.

Harry Potter 20th Anniversary: Return to Hogwarts airs on New Year’s Day on Sky Max at 8pm and streaming service NOW.

Watch: Emma Watson recalls having crush on Tom Felton while filming Harry Potter