'Harry Potter' star Alan Rickman was one of the only people who knew how Snape's story ended from 'very early' on and 'never told anyone,' according to Daniel Radcliffe

• Alan Rickman knew Snape's future during early "Harry Potter" filming, Daniel Radcliffe said.
• Not even director Chris Columbus knew what was going to happen, Radcliffe said.

Alan Rickman was one of the only people to know what laid ahead for his "Harry Potter" character Severus Snape, Daniel Radcliffe said.

During a conversation with Gary Oldman, who played Sirius Black, in the "Return to Hogwarts" 20th anniversary reunion special on HBO Max, Radcliffe said that Rickman had the "inside line" into Snape's future during the filming of the first two "Harry Potter" films.

While Snape spends much of the series as an antagonist who Harry and his friends constantly suspect of colluding with Voldemort, he reveals himself later to have been a double agent who helped protect Harry out of love for his mother, Lily.

Oldman said that he wished he would have had the "full picture" while filming, and asked if Radcliffe had a deeper understanding than other actors given that he played the series' titular character. According to Radcliffe, only Rickman did, with regards to his character.

"He very very early said to [J.K. Rowling], 'I think I need to know what happens,'" the actor said.

Radcliffe said that Rickman didn't tell anyone on set, including "Sorcerer's Stone" and "Chamber of Secrets" director Chris Columbus. When Columbus asked Rickman about an acting choice, Radcliffe recalled, Rickman would say, "I'll tell you later."

In 2011, Rickman said in an interview with the Los Angeles Times that he knew that Snape was a "double agent... and a very good one at that" from the start, despite the fact that Rowling had only written three of the books at the time "Sorcerer's Stone," the first film in the series was released.

In 2016, Rowling clarified on Twitter what she had told Rickman in order to give him a more nuanced understanding of his character: the meaning of the word "always," which Snape says after Dumbledore asks him if he still loves Lily Potter "after all this time." The special paid subtle tribute to Rickman, who died in 2016 at age 69, by ending on that line.