Award-winning comedy actress Catherine Tate was unveiled tonight as the special guest star of the Doctor Who Christmas Special: The Runaway Bride due to transmit later this year on BBC One.

Making a surprise brief appearance in the final episode wearing full bridal wear, Catherine is set to play Donna, a runaway bride, in the Christmas Special alongside David Tennant (Doctor Who).

Catherine Tate says: "I'm honoured and delighted to be joining David Tennant aboard the Tardis. I was holding out for summer season at Wigan rep but as a summer job this'll do."

In tonight's heart-breaking series two climax, Rose (Billie Piper) said a tearful farewell to the Doctor after they had been separated in parallel worlds – lost forever in time and space - following a mighty war between the Cybermen and the Daleks.

Russell T Davies adds: "Doctor Who and Catherine Tate is just the most irresistible combination, a genuine treat for Christmas viewing.

"We filmed Catherine's appearance in tonight's episode many months ago, and I'm delighted the secret is out at last! But after two years of travelling with Rose, the Tardis is in for a bumpy ride with Donna on board."

Written by Russell T Davies, the Doctor Who Christmas Special: The Runaway Bride is currently in production. The producer is Phil Collinson and executive producers are Julie Gardner and Russell T Davies.

Freema Agyeman will join David Tennant as his new companion, Martha Jones when series three begins filming in Cardiff later this month.

Shoppers in sunglasses were baffled to see Christmas trees and giant snowmen on sun-baked streets in Cardiff.

The seasonal time-trick of a frosty festive scene was created by the Doctor Who team to film the BBC show's Christmas special.

Guest star Catherine Tate braved 30C temperatures in full white bridal gown.

When fans asked David Tennant, who plays the Doctor, how he was coping he shouted back: "It's blinking boiling."

Scenes for the special, entitled The Runaway Bride, were shot in Cardiff city centre, which will be transformed into a shopping street in London's West End for the show.

Comedy star Tate, known for her catchphrase "Am I bovvered?" in her hit sketch show, might have been a little perturbed as she coped with her role as bride Donna in soaring temperatures.

She had to jump out of a black cab and run down the Cardiff street.

A Doctor Who insider revealed that audiences will see her morph into a giant bride before exploding across the screen.

She said: "I'm honoured and delighted to be joining David Tennant aboard the Tardis.

"As a summer job, this'll do."

The show's writer Russell T Davies, has joked that the Tardis would be in for a "bumpy ride" with Catherine Tate on board.

An onlooker said: "It's surreal seeing all the Christmas decorations - but it's quite nice to look at them on a hot day like this.

"It feels like the Timelord has put us in the Tardis and whisked it off for Christmas."