The character of Sgt Maj Eismayer is instantly recognisable from every basic training movie you’ve ever seen. He is the tough drill officer who humiliates and bullies new recruits, bellowing at them to hit the floor and give him 25 press-ups. But it turns out that this Austrian drama directed by David Wagner (himself an army veteran) is inspired by true events. The real-life Eismayer was a gay man who lived a double life for many years, and then fell in love with a younger colleague. The film is a surprisingly gentle, touching story about acceptance, though it is less than sizzling as a romance.

Gerhard Liebmann is brilliant as Eismayer, a man with a face chiselled out of granite and a worrying-looking vein throbbing across his forehead. He lives as a straight man, married with a young son, but sneaks off to grab quickies with men in the backs of cars. At work he is feared; “Eismayer is a total psychopath,” whispers one soldier. But then along comes recruit Mario (Luka Dimic), a gay soldier who refuses to be humiliated. There’s a terrific moment when Mario runs stark naked around the barracks, shouting: “Fairies never freeze, sergeant major sir!” Eismayer, who has lived his life in fear of exposure, cannot wrap his head around out and proud Mario.

This is an intelligent, understated and naturalistic film. The two men fall in love, then slowly it dawns on Eismayer that times have changed; he’s a dinosaur. Homophobia exists in the army but Mario is liked and accepted by his unit. Mario wants them to be a proper couple, but Eismayer says it is cloud-cuckoo-land talk: the idea of the two of them getting married at the barracks and living happily ever after. But – spoiler alert – that’s exactly what happens. The film ends with a lovely heartwarming photo of the real-life pair on their wedding day, in matching white uniforms and medals.

• Eismayer is released on 20 November on digital platforms.