London, UK - The original cast of the Harry Potter series will be reunited 20 years after the first film screened to recount their magical journeys.

An HBO Max special titled Return to Hogwarts will be released on January 1, the network has said.

Daniel Radcliffe, Rupert Grint, and Emma Watson will join American filmmaker Chris Columbus to discuss the films and explore their creation in depth.

The special will invite fans "on a magical first-person journey through one of the most beloved film franchises of all time," HBO Max said.

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The program was announced exactly 20 years on from the US release of the first movie, Harry Potter and the Philosopher's Stone, in 2001.

A 52-second trailer featured clips from several of the world-famous films and promised "the legendary cast" would return "to where the magic started."

The trio will be joined by fellow stars including Helena Bonham Carter, Robbie Coltrane, Ralph Fiennes, Jason Isaacs, Gary Oldman, Imelda Staunton, and Tom Felton.

Promoting the trailer, Felton, who played Draco Malfoy, urged fans to save the date.

"Is this what school homecoming is like?" he wrote on Twitter: "Mark your calendars for New Years Day #ReturnToHogwarts , streaming on @hbomax x."

Matt Lewis, known for his portrayal of hapless Neville Longbottom in the series, posted: "This New Year's Day... we're putting the band back together."

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Executive producer Casey Patterson said: "There's magic in the air here with this incredible cast, as they all return home to the original sets of Hogwarts, where they began 20 years ago.

"The excitement is palpable as they prepare to take their fans on a very special and personal journey, through the making of these incredible films."

It comes as Radcliffe told a BBC documentary, also marking 20 years since the first film, of his joy that many people watch the Harry Potter films when they are "hungover and feeling really crappy about themselves."

The 32-year-old said: "The time in most people's lives when they discovered it meant that it has an incredibly important place in a lot people's childhoods, and they still feel very protective over it."

"One of my favorite fates that we could never have ever imagined for the Harry Potter films but that I have been told by several friends is that they are fantastic when people are hungover and feeling really crappy about themselves."

"They will just watch back-to-back a few movies and it just takes them to a place of warmth and comfort."

"That is so lovely to me. That is the real world effect that a film can have on someone's life. I think that is great."

The documentary, as part of Movies With Ali Plumb, also saw Radcliffe pay tribute to author JK Rowling, who has expanded the Potter universe to include the Fantastic Beasts film series starring Eddie Redmayne.