The former ER star has featured intermittently on the cult sci-fi series as the Doctor's time-travelling wife, Professor River Strong, since 2008, and she will reprise the role once again to make her first appearance opposite the new Time Lord Peter Capaldi for the upcoming holiday episode.

Lead writer Steven Moffat says, "The last time the Doctor saw her she was a ghost. The first time he met her, she died. So how can he be seeing her again? As ever, with the most complicated relationship in the universe, it's a matter of time..."

A statement issued by Kingston reads: "To be honest, I did not know whether River would ever return to the show, but here she is, back with the Doctor for the Christmas special.

"Steven Moffat is on glittering form, giving us an episode filled with humour and surprise guest castings. I met Peter for the first time at Monday's read-through, we had a laugh, and I am now excited and ready to start filming with him and the Doctor Who team. Christmas in September? Why not!"

Production on the end-of-year special begins in the U.K. this week (begs31Aug15).