Some might think this is udderly asinine - but it's true.

Novak Djokovic, the champion Serbian tennis player, has bought the world's entire supply of donkey cheese.

Pule is a Serbian delicacy made with donkey's milk. It is said to be the world's most expensive cheese, which makes Djokovic's bill all the more exorbitant.

The farm's manager, Slobodan Simic, said the secret to the taste was that the donkeys were raised on one of the country's famous wildlife and nature reserves.