River Song made her first appearance on the show in 2008 and has appeared in 15 episodes to date. She also married the 11th version of the Doctor (Matt Smith), and will get to see her husband again, but in his current incarnation, played by Peter Capaldi.
"I did not know whether River would ever return to the show, but here she is, back with the Doctor for the Christmas special," Kingston said in a statement. "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?"
Added showrunner Steven Moffat: "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 ..."
Are you excited for River Song? What's your theory on how she'll return?
Doctor Who returns for its new season on Saturday, Sept. 19 at 9/8c on BBC America, and the Christmas special will air on Christmas Day, natch.
Check out the trailer for the new season: