The 10th season of Doctor Who is a one of change. The season premiere introduced Pearl Mackie's Bill, the first companion to be gay and out of the closet. At the end of the season, showrunner Steven Moffat will be stepping down after six years in charge. And Peter Capaldi will be leaving the show as well, after playing the Doctor for three seasons.

Even though the current Doctor will not regenerate until the end of the season, Capaldi has already filmed his remaining episodes, including his "death" scene. It has been rumored that actor Kris Marshall will be taking over the role -- though at this time that has not been confirmed and is still considered only a rumor. Now that all Capaldi has left to film is the Christmas Special, he has started to open up a bit about why he is leaving the show now.

While making an appearance on The Graham Norton Show recently, Capaldi spoke about why he is choosing to leave Doctor Who now:

“Doctor Who is a great job, but it is a bit of a television factory. You do twelve episodes a year, and I just worried that I wouldn't be able to continue to do my best work. I like to be able to learn the lines and do some preparation and come in and give it some vigor and not hate it. I just figure, while you're enjoying it, leave.”

When an actor is cast on Doctor Who, they know it is a temporary job. By the time the concept of the Doctor regenerating and being replaced by a new actor was added in the third season, all of his original companions had already left. The show is written in a way that allows for the cast to constantly change, based both around the needs of the story being told and the desires of the actors and actresses involved.

While there is no set rule for how long a Doctor sticks around -- Tom Baker lasted seven seasons while both Paul McGann and John Hurt had a single story each -- most actors who play the part do so for around three years. Capaldi will be the seventh Doctor for whom three is the magic number. Though due to the show's time travel elements, it's not unheard of for a Doctor to bump into an earlier incarnation of himself, leaving the door open for the actors who have played him before to return for short visits.

At this time, there is no word on how the current Doctor will "die" and regenerate into his next incarnation. Knowing Capaldi and the rest of the team behind Doctor Who, we can be sure its going to be one heck of a ride.

Doctor Who continues on BBC 1 and BBC America on April 22.

Next: Doctor Who Season 10 Premiere Review & Discussion

Source: The Graham Norton Show