Daniel Radcliffe wrote a touching tribute to 'Harry Potter' costar Alan Rickman - 'one of the greatest actors I will ever work with'

Daniel Radcliffe wrote a touching tribute to his "Harry Potter" costar Alan Rickman, best known for his portrayal of the foreboding yet complex Severus Snape in the franchise.

Rickman died Thursday at the age of 69 after a battle with cancer.

"Alan Rickman is undoubtedly one of the greatest actors I will ever work with," Radcliffe wrote in a post published on his Google+ page. "He is also, one of the loyalest and most supportive people I've ever met in the film industry. He was so encouraging of me both on set and in the years post-Potter."

According to Radcliffe, Rickman attended many, if not all, of his stage performances in both London and New York.

"He didn't have to do that," Radcliffe wrote. "I know other people who've been friends with him for much much longer than I have and they all say 'if you call Alan, it doesn't matter where in the world he is or how busy he is with what he's doing, he'll get back to you within a day.'"

The actor described Rickman as "extremely kind, generous, self-deprecating and funny," contrary to some of the characters he's portrayed. He continued, "And certain things obviously became even funnier when delivered in his unmistakable double-bass."

Radcliffe was 11 years old when he first auditioned for Harry Potter and described Rickman as "one of the first of the adults on Potter to treat me like a peer rather than a child."

"Working with him at such a formative age was incredibly important and I will carry the lessons he taught me for the rest of my life and career," Radcliffe continued. "Film sets and theatre stages are all far poorer for the loss of this great actor and man."

Other cast members from "Harry Potter" and series author J.K. Rowling took to social media to pen their own tributes to the late actor.