Scottish actor Peter Capaldi announced Monday that he will be stepping down from his role as the title character of cult favorite Doctor Who.

PETER CAPALDI LEAVING DOCTOR WHO

Capaldi began his role as the 12th Doctor in 2013 and told the BBC that it was time “to move on to different challenges.” Doctor Who has been around for decades, beginning in 1963 and running through 1989, before being rebooted in 2005. Capaldi’s last series will start in April and end around Christmas time.

The show has become a huge cult sensation with a loyal fanbase (called Whovians), and it follows a time-traveling alien simply called the Doctor who travels via the Tardis, a spaceship made to resemble an old-fashioned British police phone booth. In 2009, the Guinness World Records named it the most successful sci-fi series ever made, with an estimated 80 million viewers in 206 countries.

“I feel sad, I love Doctor Who, it is a fantastic program to work on,” said Capaldi, 58. “But I don’t know how long I can give it my best, and if I’m not giving it my best, I don’t want to do it.” The BBC requested Capaldi renew his contract with the show, but the actor declined. Executive producer Steven Moffat, who also created hit show Sherlock, said he would also be leaving the show with the same timeline.

As the show has featured many famous Doctors, now the question remains as to who will replace Capaldi and become the show’s 13th Doctor. Prior to Capaldi, Matt Smith and David Tennant played the title character. Capaldi was significantly older than his predecessors, so there is room for a completely new Doctor to emerge. Perhaps a female Doctor is in order?