Actor Christopher Eccleston has quit as Doctor Who after just one episode of the new series has been screened, the BBC has confirmed.
The first episode of the new Doctor Who was shown on Saturday
Bookies have tipped Casanova actor David Tennant as the hot favourite to replace Eccleston as the Time Lord, with odds of 1/10.
Other contenders for the role include Bill Nighy and comedian Eddie Izzard.
Eccleston's first appearance as the ninth Doctor attracted 10 million viewers.
Talks are taking place to replace him with Tennant.
A second series of the new Doctor Who, which will again be written by Russell T Davies and produced by BBC Wales, has already been commissioned.
Billie Piper, who plays Dr Who's assistant Rose, is expected to return for the second series.
David Tennant plays BBC Three's legendary lover Casanova
An initial statement issued by the BBC said Eccleston feared being typecast and had found the series gruelling - although the BBC later accepted the statement was not correct and said it had not spoken to Eccleston before releasing it.
A BBC spokesman said it had hoped, rather than expected, that Eccleston would continue in the role.
He said that although talks to make David Tennant the 10th Doctor were taking place, other names may be put forward.
Bill Nighy was also considered for the Eccleston role, while Richard E Grant starred in a BBC web adventure of Doctor Who.
Period drama Casanova, which moves to BBC1 from BBC3 on Monday, added to Tennant's reputation after his success in the drama Blackpool.
Ladbrokes spokesman Warren Lush said: "Public demand has forced us to produce a long list of possible Doctors despite the fact that David Tennant is so hotly tipped for the role.
"Before Eccleston took the role the money was for Alan Davies and Eddie Izzard and they have to be seen as possible contenders again."
However, bookmaker William Hill has refused to take any bets on the identity of the new Doctor, after being "flooded" with inquiries from people wishing to bet on Tennant.
"It appears that the BBC has moved quickly to secure David Tennant's services following the departure of Eccleston," said William Hill spokesman Graham Sharpe.
"It seems that the role is his should he want it, which makes it impossible for us to open a book."
The BBC announced on Wednesday that it had commissioned the second Doctor Who series, which will again feature 13 episodes.
Russell T Davies said: "It's fantastic news. It's been a tense and jittery time because the production team has been working on plans.
"It's particularly good for BBC Wales. This is a major flagship show for the region, and their staff and crews are the best you could find. It's a tribute to them that Doctor Who is returning."
Doctor Who was relaunched last Saturday weekend following a 16-year hiatus.
With 9.9 million viewers, it beat Ant and Dec's Saturday Night Takeaway.