Alex Kingston tells DWM:
“I spoke to Steven [Moffat] on the phone and he said, ‘I’ve got this idea and I need to know if you’re available for it, because if you’re not I can’t write this.’ I let him know when I was available and he told me the outline, but I had to swear not to tell anyone. I’m very good at keeping secrets. Matt, Karen and Arthur had guessed I knew something and tried to persuade me to tell them, but I wouldn’t! Even when we had the script for that episode, the reveal wasn’t in it. They kept those pages out so the crew didn’t know. The actors were given the single pages – I’m not even sure when. And even on shooting day, the pages weren’t there and it was only then, at the last minute, that the crew saw the reveal. They managed to keep the secret and avoid any leaks at all. That takes a lot of doing.”
The season climaxed with The Wedding of River Song (2011), a game-changer that, despite its title, left the status of the relationship between the Doctor and River up to the viewer’s interpretation. “I still get people going, ‘You’re not really married to him because he was a Teselecta!’” Alex laughs, referring to the shape-shifting craft that had taken on the Eleventh Doctor’s form. “I’m like, ‘Thank you very much, I was married to him. I’m his wife!’”