"I just landed in Lisbon and there's a castle on a hill here, so there's only one thing we can do," said the musician, in a video published on his page on Instagram.

The singer of hits including 'Shape of You' and 'Thinking Out Loud', had unexpected company during his improvised performance, but he was not intimidated.

"Singing 'Castle on the Hill' 'featuring' a seagull at Castelo de São Jorge in Lisbon before tonight's show", he joked.

Ed Sheeran was one of the headliners at the Rock in Rio Lisboa festival that took to the Palco Mundo on Sunday night.

The festival returns on 22 June in the same location with the Jonas Brothers headlining and then again on 23 June with Doja Cat being the top-billed act.