Matthew Mcconaughey calls Idris Elba ''the ass of class''.

The 'Dark Tower' actor has been poking fun at his co-star after he was named Rear of the Year last week, but after giving him the moniker he checked to make sure it wasn't a worldwide accolade.

Matthew quipped: ''He's got a trophy - the ass of class.

''Is this an English award? Is it an international ass?''

In a joint interview with 'Entertainment Tonight', Idris replied: ''It's not international, it's England. I think I'm Rear of the Year in England.

''That morning when the announcement came out, I took a good look in the mirror and I was like, 'Ok, fair enough.' ''

Matthew saw the funny side of Idris' comments about his derriere accolade, but was left speechless.

He added: ''I don't know ... I don't know what to say about that. I wasn't expecting [it].''

Tony Edwards, organiser and CEO of the Rear Of The Year Awards, admitted last week the 'Luther' star had won the prize for having a ''well-toned, firm'' behind.

He said: ''Idris is also a kick-boxer which, along with his other workouts, has ensured a particularly well-toned, firm rear.''

Tony - who awarded British TV presenter Rachel Riley with the female Rear of the Year gong - also insisted it is not always the ''biggest butt'' which triumphs.

He added: ''Both Idris and Rachel's celebrity rears represent perfect examples of today's toned and firm gluteus maximus - with quality rather than quantity as the essential fashion keynote.

''Biggest is not best when it comes to bottoms.''