Matt Smith felt the 50th anniversary year was the "right time" to leave 'Doctor Who'.
The 30-year-old actor announced in June he is quitting the sci-fi show after four years and he thought leaving after the programme celebrated its landmark birthday in November was the perfect moment.
In a video interview with Digital Spy conducted at Comic-Con 2013 in San Diego, California, he said: "I've had four wonderful years, been on some great journeys on and off screen. Part of me felt it was the right time to go after the 50th anniversary, after the celebration of its birthday, that perhaps it was my time [to go]."
The Eleventh Doctor will perish in this year's Christmas special and showrunner Steven Moffat has already told Matt how his incarnation of the Time Lord will regenerate into the Twelfth Doctor.
He teased: "I know Steven's written about 28 pages, he's pitched it to me and it sounds great. I think Steven [Moffat] is such a brilliant writer, he'll deliver something fitting and he'll write a great regeneration episode."
Matt talked through his decision to quit with Steven and his family and although it was a very tough choice, he thinks the change of lead actor will "re-galvanise" the series just as it has in the past.
Speaking to Vulture magazine, he said: "I talked to Steven about it ... Obviously that's a private conversation and it sort of has to remain that way. I have the utmost respect for him. He's a fabulous man, a great friend, and a wonderful writer ... I talked to my family about it.
"It was a very hard decision to come to because it's such a wonderful show and I love making it so much. But also, part of the value of the show is leaving at the right time and allowing someone else to take over. That re-galvanises it in a way as well. Who knows if it's wrong or right? I guess I'll know in a year's time when I'm unemployed somewhere."
The 50th anniversary special - which also stars David Tennant, Jenna-Louise Coleman, Billie Piper and John Hurt - airs on BBC One on November 23, exactly 50 years after it first started in 1963.