'Knightfall' star Tom Cullen takes us behind the scenes, into the muck

In History’s Knightfall, Tom Cullen stars as Templar Knight Landry, a man who’s put through the emotional and physical wringer as he searches for the Holy Grail in Paris in 1306. As we learned when Cullen took over Yahoo Entertainment’s Instagram leading up to the Dec. 6 premiere, filming the drama was also a test — whether he was losing a bet that required him to spend the day in his “Welsh underpants,” or losing four toenails in the freezing mud.

Knightfall airs Wednesdays at 10 p.m. on History.