Doctor Who Series 10: 11 Easter Eggs & References You Might've Missed In 'Thin Ice'

11. 1814 Frost Fair

The setting of this episode is the 1814 Frost Fair, the last ever time that such an event was held on the frozen surface of the River Thames. The Doctor is a fan of the occasion as he admits to Bill that he has been there "a few times."

He has indeed. Back in 2011's A Good Man Goes To War, River Song tells Rory that the Eleventh Doctor once took her to the 1814 Frost Fair as a birthday treat. Stevie Wonder tagged along and sung for them under London Bridge (though he wasn't aware he had travelled in time). The Twelfth Doctor also offered to take Clara to a Frost Fair back in 2014's The Caretaker.

It's possible, then, that there are three different Doctors running around on the Thames during this point in time!