'Harry Potter' 20th anniversary: trio of wizards reunite in new trailer

Full trailer for New Year's Day one-off reunion special features Daniel Radcliffe, Emma Watson and Rupert Grint

HBO released its full trailer for the eagerly awaited Harry Potter reunion special, commemorating 20 years since the release of the first film.

"Think of that powerful memory, make it the happiest you can remember," actor Daniel Radcliffe's character Harry Potter can be heard saying as the camera follows Radcliffe through a stretch of Diagon Alley, before cutting to Emma Watson walking down platform 9¾ at King's Cross Station.

The trailer for Harry Potter 20th Anniversary: Return to Hogwarts features snippets of interviews from Radcliffe, Watson and Rupert Grint.

The special is set to be available for streaming on HBO Max beginning January 1.

"It's the perfect time to sit down and reminisce," said Grint, who played Ron Weasley.

Emma Watson, who played Hermione Granger, said: "When things get really dark and times are really hard, there's something about Harry Potter that makes life richer."

Helena Bonham Carter (Bellatrix Lestrange) and Ralph Fiennes (Voldemort) shared anecdotes about playing their famous villains.

"One of the highlights of my part was when I had to pretend to be Hermione pretending to be Bellatrix," Bonham Carter said, fashioning the false teeth she wore in a scene from Harry Potter and the Deathly Hallows: Part 2.

Robbie Coltrane (Hagrid), Matthew Lewis (Neville Longbottom), Mark Williams (Arthur Weasley) and Gary Oldman (Sirius Black) will also appear in the special.

Notably missing will be author JK Rowling, who made controversial remarks on transgender issues last year. It is unclear if those remarks are related to her absence.

The Harry Potter franchise is one of the most profitable in history, drawing in $8.5 billion at the box office worldwide, according to data from Statista. More than 500 million Harry Potter books have been sold.