George Clooney bought kitchen staff a bottle of his own tequila at his wife's birthday celebrations last Friday.

An onlooker told People magazine the quartet drank Casamigos tequila - a brand owned by George, Rande, and Mike Meldman - and when they filled out the dessert menu, they checked a box at the bottom which said "Buy the kitchen a six pack of beer."

However, they crossed out the words "six pack of beer" and wrote "bottle of Casamigos" instead.

Rande recently revealed he and George were "forced" to make Casamigos available for sale because they were consuming so much themselves.

He recalled: "George and I started drinking tequila a very long time ago...

"There came a point when George said to me, 'Why don't we just make our own.' We never meant it to be a business.

"We started out just us drinking it, without anyone being able to buy a bottle.

"We were kind of forced into [making it a business], after about two years, we got a call from our distillery and they said to us, 'We have a situation. For the past two years, we've sent you a thousand bottles a year. Either you're selling it, or you're drinking way too much. You need to get licensed and get legit with the situation.'

"We drink a lot but we were giving it to friends and they liked it and gave it to their friends."