The 8-1 shot soared over the last of the 30 jumps and bounded clear to victory down the home straight.
Vanillier closed slightly before finishing second with Gaillard Du Mesnil in third place.
For winning jockey Fox it was his second victory in the iconic steeplechase and came after he needed a late fitness test to be declared fit to ride.
"He is just a phenomenal horse. I can't believe it. He normally gets his head up a wee bit but today he travelled everywhere," he said.
"He is the cleverest horse. He is so intelligent."
The start of the race, one of the highest-profile events in Britain's sporting calendar, was delayed for around 15 minutes after animal rights protesters made their way on to the course.
Some tried to attach themselves to fences before they were dragged away by police.
