10 Doctor Who Secrets That Were Hiding In Plain Sight
2. The Cybermen Cameo In A Painting (The Day Of The Doctor)
The Day of the Doctor features several paintings that are brought to life as the Zygons utilise 3D art to invade present-day Earth. The paintings themselves are stored in the National Gallery's Undergallery, curated by a future version of the Doctor.
Another painting stored in the Undergallery is The Raft of the Medusa, but with a twist. This painting can be seen behind Clara while the Eleventh Doctor is trying on his latest fez, and it's not immediately clear that this isn't the version of The Raft of the Medusa that art scholars would recognise.
That's because the real-life shipwreck depicted in the painting is fully crewed by... Cybermen! Clearly, there's an unseen celebrity historical in which the Doctor teams up with a French painter to halt a Cyberman invasion.
It's a clever flourish by Doctor Who's production designers, given that hiding aliens inside paintings is the plot of The Day of the Doctor. As the three Doctors have to contend with Zygons and Daleks, it's a good job that the Cybermen didn't also join the party – but it's fitting that they did at least appear, to celebrate the show's 50th birthday.