Freema Agyeman on the 'big secret' of the Doctor Who cliffhanger

ACTRESS Freema Agyeman has spoken about the challenge of guarding the secret of tomorrow's Doctor Who season finale.

Last week, millions of viewers watched as David Tennant's Time Lord started to regenerate after being blasted by a Dalek death-ray. Speculation has been rife about whether he's leaving the show and whether we are going to get a new Doctor.

Freema, 29, plays Martha Jones, a previous companion of the Time Lord who returned for this end-of-series storyline involving a Dalek conquest of the Earth. She told BBC Radio 4 it hadn't been easy to keep tomorrow night's conclusion under wraps.

She said: "It's been a big secret to keep. People have been coming up to me in the street and asking if David Tennant is leaving and if we are going to get a new Doctor. Tomorrow that question will be answered and I can relax."

Doctor Who returns for its fifth series in 2010. In the meantime, there will be a Christmas special this year and four further specials during 2009.

Since last weekend's bombshell episode, writer and executive producer Russell T Davies has been unavailable for interviews. He is leaving Doctor Who after this series and told Radio 4 the key to the show's success had been that it was "intelligent but fun."