Tom Cruise's highly anticipated suspense thriller 'Valkyrie' finally arrives in theaters December 26, and ET's own Mary Hart is with Tom, director Bryan Singer and co-stars Carice van Houten and Thomas Kretschmann to get their take on the true story and "what if" scenario that could have changed the course of World War II!

In 'Valkyrie,' Tom plays Col. Claus Graf von Stauffenberg, who helped to hatch a plot to assassinate Adolf Hitler at the height of the war in order seize power and put an end to the bloodshed.

"He was a man who thought beyond himself and even his country, looking toward the world," says Tom. "Very early on he was someone who opposed Hitler."

The question posed on everyone's mind at one point or another, adds Tom, is why didn't anyone just go ahead and just shoot Hitler? Well, it wasn't that easy, explains Singer.

"You have millions of people in the army: 3,000 generals, German generals in the field; you've got fanatical Nazis working all around them, and a government that was about getting rid of him, but also [about] turning the government around," he says. "['Valkyrie'] was a very ambitious plot, and all the soldiers had taken an oath to [Hitler] personally. It's very serious."

Things weren't always so serious on the set, however, as the cast and crew tried to keep things light despite the dark subject matter -- and sometimes the location itself provided the entertainment.

"We had to stop shooting [one day] because there was a wild boar in the neighborhood," says Tom with a laugh. "That was a new one. I thought I was being 'Punk'd.'"

In the interview with Mary, Tom also showed off his new shirt designed specifically for him by Katie Holmes for their wedding anniversary, and revealed what daughter Suri thought when she saw her dad on set wearing an eye patch for the movie!

"The make-up girls are smart -- they got a teddy bear with a patch," says Tom. "She got used to that, [but] first when she saw [me with it] she would come up and take the patch off my face."

Watch ET for more with Tom and 'Valkyrie'!