The Polar Express is a Christmas movie classic, but did you know it features an incredible Back to the Future Easter Egg?

The reason is that both movies were directed by Robert Zemeckis, who inserted that blink-and-you’ll-miss-it nod.

Film fans will remember at the end of Back to the Future Part III when Doc Brown and his family fly off in their steam-powered time-travelling train.

Well, in The Polar Express, the titular locomotive also appears to be a time machine.

We know this because a flux…