As the Doctor's wife, she became one of the most beloved characters of all time, meeting various different incarnations of the Time Lord in the wrong order.
Celebrating the show's upcoming 60th anniversary, the actress answered some burning questions from Doctor Who fans - and, staying true to character, revealed that she's holding some pretty big spoilers in.
Are you keeping any juicy spoilers right now?
Submitted by @MatthewVernon3
"Am I keeping any juicy spoilers right now? Yes, I am actually, I'm keeping a juicy spoiler! Yes, that will be revealed, I would imagine, later in the year..."
What's your favourite aspect of River Song?
Submitted by @telzeyamber
"She has the most fantastic one liners. I think it's her her naughtiness, but always ultimately, her love. She has this unconditional love for the Doctor - but she she can also be naughty."
What shenanigans did River and the Doctor get up to on Darilium?
Submitted by @SpencerTracyFan
"Oh my gosh! No, that's a big spoiler."
What's it been like working with all the different Doctors at Big Finish and how has that developed River's character?
"The community at Big Finish have also become a family. I've worked on a lot of stories over the years and it's, it's just so much fun. The freedom, actually, that you have with audio is quite extraordinary, because of course, the writers can really go to town with their imagination, because they don't need to think about filming budgets or anything like that and you're just in a sound booth and you have to create that world then alongside all the special effects that are edited on to the story afterwards.
"It's been really fun and I've been able to work with all of the Doctors. And also we've been able to just take River Song's diary and run with that and have a whole different set of stories where she's actually living her own adventures, living through her own adventures without the Doctor because, of course, that was one of the things that I would always kind of think about was 'what's River doing when she's not having an adventure with a Doctor'?
"Obviously she's up to something and knowing her personality, she wouldn't sort of just be sitting at home mopping the floors or knitting or something! She would be off. And so I love the fact that we've been able to sort of investigate her life away from the Doctor."
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What was your favourite scene or episode to film?
Submitted by DannyFlavs17
"I've been amazingly lucky because Steven Moffat wouldn't allow any of the other writers to write for my character. So the only episodes I had ever been in were episodes written by Steven, and I always felt that I had the best lines. And in fact, Matt would always sort of grudgingly say 'Yes, you do have the best lines'.
"So it's very difficult for me to be able to actually say I have a best episode, because I feel that it would somehow make it seem as though I felt the other episodes weren't as good or were lesser in some way. And that's not the case.
"Every single episode that I was in was an absolute joy to film and we had so much fun on. But I mean, yes, for sure. The very first episode I was ever in has to be for obvious reasons, and also the Husbands of River Song, that moment with Peter Capaldi when I suddenly realise who he is.
"That was such a hard moment to film because I had to – I knew obviously, as Alex – but I had to not know as River Song who he was until he says 'Hello, sweetie'. It was just very hard emotionally to kind of like, stay innocent of the of the knowledge.
"I loved doing Let's Kill Hitler. I loved that episode because it was just so out there. I mean, I don't know what goes on in Steven's brain. He's an absolute genius. But no, it was brilliant. I mean, who doesn't love a banana?!
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