Watch: Justin Bieber serenades fiancée outside Buckingham Palace

Tourists who amassed in front of Buckingham Palace on Wednesday were probably hoping to get a glimpse of the British royal family — but instead, got treated to a show from pop royalty.

Justin Bieber was spotted sightseeing in the British capital with model and fiancée Hailey Baldwin when he whipped out his guitar in front of the Queen's official residence for an impromptu rendition of his 2016 hit, Cold Water.

Despite his best efforts to go incognito in an oversized hoodie, Bieber's serenade to his fiancée did not go unnoticed and quickly drew a crowd who were happy to record the event for posterity and social media.

The Canadian pop sensation, 24, and Baldwin, 21, sparked speculation that they had married last week after they were pictured entering a New York Court house where marriage licences are issued.