Catherine Tate has suggested that the next series of Doctor Who could be the last for actor David Tennant.
The comedian, speaking on Radio 2's Jonathan Ross programme, said: "I think it's maybe David's last series."
The BBC refused to comment on Mr Tennant's future as the show's star.
Tate, who first appeared in the 2006 Christmas special, is to return as the doctor's assistant, Donna, for the entire run of the fourth series.
She will also be joined for several episodes by the doctor's former companion Martha Jones, played by Freema Agyeman.
When pressed on whether Tennant would return to play the timelord in special Dr Who shows in future, Tate replied: "Possibly."
The comedian also confirmed that the forthcoming series would be her last.
Tate made her Doctor Who debut last year as a runaway bride who found herself transported into the Tardis as she prepared for her wedding on Christmas Eve.
The episode attracted an audience of 9.4 million when it was screened on BBC One on Christmas Day.
This year's Christmas special, starring Kylie Minogue, is due to be screened at 1850 GMT on 25 December.
Speaking to Doctor Who magazine, the pop star said appearing in the show was "like stepping back in time".
"I really felt at home being back in the world of TV," she added. "I've definitely got the acting bug again!"
If David leaves, I'll be so broken-hearted. He's so wonderful as the Doctor. Of course, he can't play the part forever. I'll just have to look forward to all his future projects.