The King accepted the offer to enjoy “a slurp” of beer after pulling himself a pint during a visit to a brewery in Staffordshire.
The 76-year-old was at the family-owned Tower Brewery in Burton Upon Trent.
After the King pulled a pint called Gone For A Burton, a traditional mid-strength beer brewed by Tower, brewery owner John Mills cheekily asked him: “Going to have a slurp of that, sir?”
The King replied that if he was not, he was in the “wrong place”.
Then, as he held up his pint, he said “to your very good health,” before joking “I could pass the rest on to them”, as he looked at the gathered media.
Mr Mills joined the King at the brewery’s bar, pulling himself a pint of his Imperial IPA in the town from where India Pale Ale was first exported in the 1820s.
He then suggested they try something stronger.
Behind them was a bottle of The Spirit Of Burton, a 41% proof Tower spirit distilled from IPA which, if left to mature, would be the basis of whisky.
After taking a sip, the King, who is known to like whisky, seemed to approve and said “interesting – yes, it’s supercharged”.
The monarch also visited the world headquarters of JCB in Staffordshire to mark the construction equipment company’s 80th birthday.
He met employees, apprentices and their families and toured the factory in Rocester.
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The King helped to fit a tyre to a backhoe loader, a digger invented by JCB’s founder, the late Joseph Cyril Bamford CBE.
The visit also marked the production of the one millionth backhoe digger, which is said to have replaced men with shovels and pickaxes.