Doctor Who show runner Steven Moffat has hinted that River Song and Captain Jack Harkness could be making a reappearance in the show.
Alex Kingston last appeared as time traveller River in the hit sc- fi series in 2013, while John Barrowman's action hero character Jack - who also starred in spin-off show Torchwood - has not been seen in Doctor Who since 2010.
But speaking to TV blog Zap2it, writer Steven revealed it is possible both characters could be reunited on screen with the Time Lord in an upcoming series.
Steven said: "It's never, ever closed off. It's all about 'Do you have a story that's worth it?' Unless you've got a story that is absolutely informed and invigorated by their presence, just bringing a character back in an ordinary story won't do."
He added: "Both River Song and Jack Harkness are massive characters in Doctor Who mythology. Their returns would have to be seismic, not routine."
But Steven insisted he would not write Alex and John cameos in the show just for the sake of it.
He said: "Sometimes you have to know when a story's over, you do. One of the things you always want to say is 'leave them wanting more'."