How to get a teenager to clean his room

I am sure tis is a very universal question - how to get your teenager to clean up his room?!?!
So far nothing has worked, we tried all sorts of parental techniques but failed, and came to the conclusion that said teenager just likes to live messy and urm - once he moves out - of house - eventually -- it will be his flatmates or partners problem to sort. So you can imagine the total shock at dinner time when said teenager calmly announces that this coming week during the school holidays his major goal is to clean up his room!! -
WELL - it took another hour or more for him to come clean!! Seems a girl (whom we know and he keeps stressing - they are just friends!!!) is visiting at the end of the week.

Hmmmm wonder if we should invite the young lady round once a month ? ? ? :D (A)

Anyhow I am on the most strict instruction, not take a photo of said teenager who will be wearing a pinnie and do the cleaning. (Thank goodness there is photoshop) - Since when did I listen . . . .

Mind you he cuts a fine figure and does wonders in the kitchen - which doesn't do much for MY figure!!