The Husbands of River Song may have been all about Song's meeting with the Twelfth Doctor, but Matt Smith's previous incarnation wasn't forgotten, with a blink-and-you'll-miss-it reference to the Eleventh Doctor towards the start of the Christmas special. 

The moment comes as River is frantically trying to empty out her bag in order to fit in the head of King Hydroflax. And what does she chuck out to make room? A plate and... a fez! 

Yep, it's the Eleventh Doctor's favourite bit of comedy headwear. 

When you discover where we are in River's timeline, it makes a lot of sense that she has suddenly become sentimental. Her diary is nearly full, after all, and it's revealed that the Twelfth Doctor is meeting her shortly after the events of The Angels Take Manhattan, where she and Eleven witnessed the end of the Ponds. 

Adding to the Eleventh Doctor nostalgia, other Matt Smith adventures also get a shout-out, with maitre d' Flemming referencing The Crash of the Byzantium and – everyone's favourite – Jim the Fish when reading from Song's diary. 

Even our new Doctor hasn't forgotten about his former self, with a cheeky chin mime to remind us of that old Dick Dastardly face. 

Aw.