After the terrible news that Alan Rickman died at the age of 69, fans are appreciating his legacy of excellent cinema roles.

He may be best known as the enigmatic Snape in the “Harry Potter” films, but he will always be remembered as one of, if not the greatest, action-movie villains of all time in “Die Hard.”

But one thing Rickman’s fans may not know is the true reason for his shocked expression as he falls to his death in Die Hard.

The sequence in which McClane utters his final words to the villain, who subsequently falls from the building with this horrified response, is the most cited and replayed scene in the film.

Rickman was a fantastic, one-of-a-kind performer, but there’s more to the tale behind that reaction shot than simply acting.

On the count of three, director John McTiernan requested Rickman to fall backwards onto an airbag from a height of 25 feet. Sounds simple enough, until the stunt team opted to drop him on “one” instead, in order to make his response more realistic. So now you know why Hans Gruber’s look is so priceless.

That’s right: Rickman kept it real in his finest movie shot ever, even if it wasn’t precisely what he planned.

Rickman was apparently displeased by the ‘surprise’ drop (as would anybody) because he was already concerned about the stunt’s safety.

Daniel Radcliffe recalls being terrified of Alan Rickman On the set of ‘Harry Potter.’

When Daniel Radcliffe was cast in the big-screen version of J.K. Rowling’s enormously successful Harry Potter novel series, he was still young. So it’s understandable that the 11-year-old was afraid of Alan Rickman, the late Die Hard baddie cast as Harry’s obviously menacing opponent, Severus Snape, in the early days of the film franchise.

“He was very intimidating at first, when you first met him on set,” Radcliffe said when promoting his own evil role in the upcoming sequel Now You See Me 2. “I remember being really scared of him when I was younger. And then you suddenly realize when you’re like 13 or 14 that he’s not scary, really. He’s just got a really deep, really intimidating voice. And he’s actually really funny and self-deprecating and vulnerable and all this stuff that you don’t expect.”