BBC’s sci-fi stalwart “Doctor Who” ran for twenty-six seasons during its initial run, while the revival series has racked up an impressive nine seasons to date along with numerous specials and a tenth season on the way early next year.

Current showrunner Steven Moffat has been in charge of the ‘Who’ revival since the fifth season, the first year that Matt Smith took on the role. During that time he’s also been in charge of the BBC’s “Sherlock” which has led to him being frequently very busy. Though he’s tried to keep both shows going as smoothly as possible, he admits that of the years he’s worked on the show that it was the seventh season spread across 2012 and 2013 that were the nadir of his time on the show. He explained to Doctor Who Magazine (via Cult Box) it was a case of simply taking on too much:

“The workload was just insane. I wasn’t coping as well. No-one else’s fault, all mine. The 50th was looming, and I didn’t know if we could make it work. It was a tough, tough time. My darkest hour on Who was that. Matt [Smith], who was a friend and ally, was leaving — I couldn’t get him to stay. It felt like everything was blowing up around me. I was staggering into the 50th [anniversary special], with no Doctors contracted to appear in it, battered with endless hate mail about how I hadn’t got William Hartnell back… and Sherlock series three at the same time.”

The seventh season saw major creative shifts, such as the changing of companion to the departure of Smith which came as a surprise to many. Moffat added that couldn’t let his tenure end on such a note which is why he stuck around for Peter Capaldi’s launch with the recent ninth season drawing solid acclaim for some of its episodes.

The upcoming tenth season will be Moffat’s last on the show with Chris Chibnall taking over for the eleventh season. Our first glimpse at season ten comes with a Christmas special this year which will boast a guest companion. Pearl Mackie’s Bill, the new companion, will be introduced at the start of season ten in early 2017.