They are a household name in international boxing; they speak four languages; they have PhDs and one of them is an anti-corruption politician in Ukraine, so perhaps a film about the Klitschkos was inevitable.

Klitschko is a feature-length documentary by German director Sebastian Dehnhardt, who followed the brothers around with a camera for two-and-a-half years, after they finally agreed to let him into their lives.

It documents the Klitschkos' rise from their tough, Soviet upbringing to world champion boxers, and discusses why they are not just icons in their native Ukraine, but all over the world - their fights draw audiences from over 100 different countries.

But Klitschko also focuses on the negative side of their lives, including the agony of defeat, bad press and the moment Wladimir kicked Vitali out of his training camp following a row.

It features never-seen-before footage in training camps, changing rooms and even inside the house they spent some of their childhood in on a Kazakh military base.

The Klitschkos’ parents have been interviewed for the first – and perhaps last – time for the film, giving a glimpse into what a caring mother feels when her sons are in the ring.

Dehnhardt knows what fans of the Klitschkos want to know though, and doesn't shy away from asking the question: will they ever break their promise to their mother never to fight each other?

Klitschko is currently out in select Empire cinemas and will be available on Blu-Ray and DVD from May 28.