As it turns out, it was McKellen's choice not to take on the mantel.
Actor Richard Harris originated the role of the celebrated Hogwarts headmaster in the first two Harry Potter films, but he died after a battle with Hodgkin's disease in 2002, at the age of 72, before the start of production on Harry Potter and the Prisoner of Azkaban.
While filmmakers ended up casting Michael Gambon in the iconic role for the next six films in the series, producers first approached a number of famed English actors, including McKellen.
"When they called me up and said would I be interested in being in the Harry Potter films, they didn’t say in what part," McKellen recounted. "I worked out what they were thinking, and I couldn't… I couldn't take over the part from an actor who I'd known didn't approve of me."
McKellen's explanation was in response to a comment Harris made years ago in which he criticized McKellen -- as well as actors Kenneth Branagh and Derek Jacobi -- for being "technically brilliant but passionless."
However, despite turning down the role, it sounds as though McKellen occasionally wonders what could have been if he had decided to portray the iconic character.
"Sometimes, when I see the posters of Mike Gambon, the actor who gloriously plays Dumbledore, I think sometimes it is me," the 77-year-old Golden Globe-winning screen legend