George Clooney jumped behind the bar and hawked his billion-dollar booze brand at the royal wedding reception.

The star — who attended the nuptials with wife Amal Clooney — was serving up shots of his Casamigos tequila at the event and was also spotted whisking the bride away for a dance during the party.

Said a party source: “Clooney got behind the bar and was making cocktails for everyone.”

We hear the royal connection to the brand (which Clooney and Rande Gerber sold to Diageo last year) is Jack Brooksbank — the fiancé of Prince Harry’s cousin Princess Eugenie.

Soon-to-be-royal Brooksbank has been a UK brand ambassador for the tequila since 2016.

He’s also the former manager of the London nightclub Mahiki, and ran the racy Mexican-themed Tonteria, co-owned by another guest at the wedding, Guy Pelly, who is a close friend of Harry’s.

Daughter of Prince Andrew and Sarah Ferguson, Eugenie will marry Brooksbank in October in St. George’s Chapel at Windsor Castle, the same venue where Harry and Meghan Markle tied the knot on Saturday.

Eugenie and Brooksbank last month also moved in next door to Harry and Markle within Kensington Palace, and reports said the couples have become quite close.

Eugenie is ninth in line to the throne and had been living within St. James’s Palace with sister Princess Beatrice.

A source added of Clooney’s royal bartender role, “He did the same thing at the London launch” for Casamigos at the Beaumont Hotel in 2015, and “George also often gets behind the bar at Café Habana in Malibu,” owned by Gerber.