By Lizo Mzimba
Entertainment correspondent, BBC News
Matt Smith is the youngest actor to take on the role
New Doctor Matt Smith is simply "the best", according to Steven Moffat, head writer of the 2010 series of Dr Who.
Smith, who is the 11th actor to play the Time Lord on TV, will take over from David Tennant in the lead role of the long-running show next year.
Dr Who is one of the BBC's most popular shows and Moffat is under a lot of pressure to continue its success.
"What if I broke Doctor Who? That would be a tragedy," he said at the 2009 Screenwriters' Festival in Cheltenham.
"Yes, you do feel [the] pressure," he added.
Filming began in July on the new series of the time travel saga.
Moffat who is writing six of the episodes and overseeing another seven, promised fans "great stories" and said there would "joyous moments" as well as "heartbreak".
David Tennant and Russell T Davies on their final adventures with Doctor Who
The screenwriter is currently working on the script for the climax to the series for which expectations will be huge.
"[My] biggest challenge right now is the writing of Episode 13," he confessed.
But he had nothing but praise for Matt Smith - at 27 the youngest actor ever to play the 900-year-old Time Lord.
"He's all the things you'd expect, including ancient," he revealed, describing the new Doctor as "someone you can't take your eyes off".
It's not only the Doctor who'll have regenerated in the new series. The Tardis has also undergone a significant makeover.
"There is a plot reason for it," Moffat confirmed.
"I always liked the Tardis from the Peter Cushing [Dr Who] movies, and wanted to make it more like that".
Moffat, whose TV work includes Press Gang and Coupling, has written for Doctor Who since it returned to TV screens four years ago.
He penned the episode Blink, featuring killer stone statues, which fans recently voted the second-best Dr Who episode, in a poll conducted by Dr Who Magazine.
The Waters of Mars, the first of David Tennant's final three adventures, will be broadcast in November.
His final story, The End of Time, in which he will regenerate into Matt Smith's Doctor, has yet to be scheduled, but is expected to air at the end of 2009 or very early in 2010.