It's been teased before in the show and the "Doctor Who" season 9 Christmas Special will finally show it. Executive producer Steven Moffat said fans will finally see the Doctor (Peter Capaldi) and River Song (Alex Kingston) "at the height of their power."
Moffat sat down with Radio Times to talk about this year's Christmas special.
"One thing worth saying about it is, if you're a long-term fan of the show, you might be interested because there's been a lot of talk about the Doctor and River's glory years but we've never seen them," he said.
"Here at last we see them as Mr. & Mrs. Who at the height of their powers. It's great fun."
Elsewhere, the showrunner revealed the season 9 Christmas special will have a lighter tone than last year's. Moffat saw the opportunity to use it "to take [the tone] back up" given the finale's dark tone.
The 54-year-old also revealed he brought River Song back to "Doctor Who" because going straight to a new companion "[is] not right." He also thought the Christmas special would be his last episode.
"I thought it might be the last one, so to get River in - that was bringing me full-circle," Moffat told Digital Spy.
Moffat went on to admit he loved writing the character and the idea of her return "cheered [him] up."
As for when the special happens in River's timeline, Moffat told Radio Times it's right after 2012's "The Angels Take Manhattan" where the Eleventh Doctor (Matt Smith) lost Amy (Karen Gillan) and Rory (Arthur Darvill) but before 2013's "The Name of the Doctor."
Speculation followed what River's comeback might imply but thankfully, the BBC has released the Christmas special's official synopsis. Read it here, courtesy of CarterMatt.
The "Doctor Who" season 9 Christmas special, "The Husbands of River Song," airs on Christmas day at 5:15 p.m. on BBC One.
