Like many, Christian Bale knew little about the Armenian genocide when he signed on for the World War I drama The Promise.

The Turkish are squeamish about the word genocide – in fact it wasn’t until 1943 that the word was invented by Polish-Jewish lawyer Raphael Lemkin, applying it to the Jews in Nazi Germany.

But the facts cannot be denied. On the eve of World War I there were two million Armenians in the crumbling Ottoman Empire, and by 1922 less than a quarter remained.

As David Fromkin put it in his chronicle of World War I and its aftermath, A Peace to End All Peace, “Rape and beating were commonplace. Those who were not killed at once were driven through mountains and deserts without food, drink or shelter. Hundreds of thousands of Armenians eventually succumbed or were killed.“

Director Terry George was tasked with bringing this shameful chapter of Turkey’s history to light in The Promise, sweetening the bitter tale with a love triangle involving Bale’s American journalist, Charlotte Le Bon’s beautiful Ana, and Oscar Isaac’s Armenian medical student.

“I was stunned and a little embarrassed that I’d never heard anything about the Armenian genocide,” recalls Bale when STACK meets with him. “One and a half million people slaughtered, and I didn’t know about it, and found that most people didn’t know about it either? I hope that in some way this film can help to right that wrong.”

Slowly the world is waking up to this story. “It’s starting to happen,” says Bale. “People became aware with the 100th anniversary, and then you have world leaders who start to acknowledge and recognise it; the Pope has done that. As of yet, no sitting US President has done that, and largely that’s because of Turkey’s strategic value, but it’s an absolute pivotal moment in history, and the lack of consequence no doubt led to the Ukrainian genocide, and the Holocaust, and Cambodia, and Rwanda. I was just watching on the news the Yazidis being slaughtered as well. So it continues to this day, which makes this film very relevant,” says the Welsh-born actor, best known for his role as Batman in Christopher Nolan’s trilogy, as well as for blowing his fuse on the odd occasion.

If Bale has been largely absent from the big screen since his Oscar-nominated performance in The Big Short, then he’s been busy filming The Promise on locations around Spain and Portugal, and will also soon be seen in the western Hostiles, playing an army captain in Cheyenne territory.

Wed 17 years to make-up artist Sibi Blazic with whom he has daughter Emmaline, 12, and son Joseph, 3, this versatile actor says it’s hard to leave his family for the movie set.

“What I am most proud of is time with my children, because that’s the most precious thing isn’t it? Time with my children, my family, my wife, and being able to achieve that because, cliché as it is, you watch your children grow up so bloody fast. One thing that happens to a lot of film people is that they’re away travelling so much, and then they come home and realise that their children are all grown up.

“So I fight against that all the time. Also I have no problem in saying no to work. I work when I really have no other reason to say no to something, and I sort of go a little bit kicking and screaming. I love it when I get there, but the anticipation of it is always something I dread,” admits Bale, 43, who won an Oscar for The Fighter as well as delivering powerful performances in The Machinist, American Psycho and American Hustle.

If fans are used to him piling on the weight or losing it for his many roles, he scaled back in The Promise. “Looking at the men of that era, lots of them liked really extravagant facial hair. But I didn’t go with extraordinarily extravagant because Terry, rightly, didn’t want me to distract.”

For his future roles, he sees a less extreme approach to physical transformation. “My body started rebelling against me with all that. I’ve always treated my body like a tool for my craft so now perhaps there are limits to how often you can do that.”

The Promise is in cinemas June 15.