Justin Bieber serenades Hailey Baldwin outside Buckingham Palace

Video caption, Bieber performed the impromptu gig with his acoustic guitar

Justin Bieber surprised fans by serenading partner Hailey Baldwin outside Buckingham Palace in London.

The pop star performed acoustic versions of Cold Water, his 2016 collaboration with Major Lazer and MO, and Tracy Chapman's 1988 hit Fast Car.

Image source, Beretta/Sims/REX/Shutterstock

Image caption, Baldwin watched on as Bieber sang at the foot of the Victoria Memorial

Baldwin watched with fans and proudly filmed on her phone.

The couple did some sightseeing after flying in for Baldwin's catwalk show during London Fashion Week, and were also spotted near the London Eye.

Image source, Getty Images

Image caption, The model curated her second Fashion Week show with Adidas and JD

Last week, it was rumoured that Bieber and Baldwin had secretly married after they were seen in a New York City courthouse.

The model denied the rumours on Twitter in a now deleted tweet in which she wrote: "I understand where the speculation is coming from, but I'm not married yet!"

But on the red carpet for Monday's Emmy Awards, Alec Baldwin was asked about his niece's engagement and said they are already husband and wife. "They just went off and got married," the actor told .

The rumours of the couple's marriage come two months after the pair got engaged in the Bahamas.

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