Barack Obama is so close to David Cameron that the US President calls him "bro", the Prime Minister has revealed.

Speaking to The Mail on Sunday, Mr Cameron described the famously “special” relationship between Washington and Westminster as “stronger than it has ever been, privately and in public,” and that during phone calls Obama refers to him as “bro”.

For those less well-versed in youth vernacular, the Urban Dictionary helpfully defines the term as describing “an alpha male idiot” or “obnoxious partying males often seen at college parties”.

“Bro” may also describe a type of bra designed specifically for men.

However, perhaps it should be assumed Obama uses it as a term of endearment, to mean close pals or “brothers”.

Either way, it can be seen as a step forward from George W Bush’s condescending idiom: “Yo, Blair.”

As if we needed any more proof of the blossoming bromance, here are some pictures of the transatlantic “bros” looking all buddied-up.

The pair chuckling away at this year's G7 Summit in Belgium (Getty)

The boys are at it again during this year's G20 Summit (Getty)

A classic practical joke by Cameron at the Nato summit in 2012 (Getty)

Team work makes the dream work: the two 'bros' playing table tennis at the Globe Academy School in London, 2011 (Getty)

The famous selfie taken at Nelson Mandela's funeral