The 13th incarnation of the Time Lord will replace Peter Capaldi in the episode 'Twice Upon a Time' on Christmas Day.

The world’s longest-running science-fiction TV series, BBC’s Doctor Who, is set for a historic moment in its upcoming Christmas Special, which airs around the world Dec. 25.

Titled Twice Upon A Time, the one-hour episode will, for the first time in the show’s 54-year history, introduce a female to play the lead role of the Earth-loving time traveler. 

John Hurt (Alien), David Tennant (Jessica Jones) and Matt Smith (The Crown) have all portrayed the mysterious Time Lord known as “The Doctor” since the show’s 1963 launch. Oscar-winner Peter Capaldi is currently playing the part of the Twelfth Doctor.

Christmas Day 2017 will see the debut of Jodie Whittaker as the Thirteenth Doctor.

The actress made an impressive debut in the 2006 feature Venus opposite Peter O’Toole and went on to star in the St Trinians movies and Joe Cornish’s Attack the Block (also starring Star Wars’ John Boyega). But it was on the small screen where Whittaker was established as a name in the U.K. with three seasons of Broadchurch, from new Doctor Who showrunner Chris Chibnall.

But how will Whittaker be introduced to the world as the Thirteenth Doctor?

Twice Upon a Time finds the Twelfth Doctor fighting his regeneration (he was fatally wounded in the Doctor Who Series-10 finale earlier this year) and unwilling to change into his new persona. But, after meeting his former self, the First Doctor (here played by Game of Thrones’ David Bradley), the Time Lord gives in and regenerates alone in his time-traveling ship, the TARDIS.

This is another unusual move for the show as the Doctor tends to regenerate with an audience (his companions), but Whittaker's new Doctor will find herself alone in the TARDIS console room.

Millions of Whovians will be anxiously awaiting the first words from Whittaker’s Thirteenth Doctor, which will close the episode. The opening salvo from the new Doctor is something of new tradition in recent years, with Tennant, Smith and Capaldi all delivering memorable (and usually on the funny side) first lines.

Outgoing showrunner Steven Moffat (also responsible for Sherlock) has already commented that Whittaker’s debut in the story instantly made him laugh.

However, pre-2005, only one of the incarnations actually spoke immediately post-regeneration (in this case, Colin Baker’s Sixth Doctor in 1984). Perhaps new showrunner Chibnall will take the more traditional route and leave us all waiting until the Fall to hear her first words?

Historically, the Christmas Special itself was actually non-existent until Russell T Davies rebooted the show, introducing Doctor Who to a whole new generation in the Noughties.

In its first 26 years, only one episode of Doctor Who fell on Christmas Day:1965’s appropriately-titled The Feast of Steven (part of a 12-part serial, The Daleks’ Master Plan) was set on Dec. 25 and, in a moment of festive frivolity, William Hartnell’s Doctor turned to the camera and announced, “Incidentally, a Happy Christmas to all of you at home!”

Capaldi is not expected to attempt this during the forthcoming episode, Twice Upon A Time.

Whether or not Whittaker does is yet to be seen.

Doctor Who: Twice Upon A Time airs on BBC AMERICA on Dec 25, 2017.