American dignitaries had a surprise on a trip to Belfast on Friday as their visit to City Hall coincided with a wedding party dressed entirely in onesies.

US ambassador to the UK Robert Wood Johnson and lord mayor Deirdre Hargey were pictured alongside 20 guests dressed as animals, Simpsons characters and dinosaurs as the partygoers mingled with senior diplomats in the lobby.

The ambassador showed his sense of humour, however, chatting with the revellers and telling the Press Association: “Boy, I wanted to join that one – I needed my costume.”

US ambassador to the UK Robert Wood Johnson chats with wedding guests in onesies at Belfast City Hall (Credit: David Armitage/PA)

Belfast city councillor David Armitage caught the scene on camera as he was heading into City Hall.

“I turned around and saw the Simpsons wedding and thought ‘this is going to be interesting’,” he said.

“Everything seemed to be very good-natured, though, and the ambassador took it in his stride.”

Asked if he had ever seen anything like it before, Mr Wood Johnson replied: “No. That’s unique.”

“I may do that myself,” he added.

Northern Ireland US consul general Elizabeth Kennedy Trudeau, Belfast lord mayor Deirdre Hargey and the US ambassador to the UK Robert Wood Johnson outside Belfast City Hall (Credit: David Young/PA)

Ms Hargey joked she timed the visit to coincide with the wedding.

“We said when you come to Belfast you can have a bit of banter and craic and no better way to do it than at a wedding,” she said.