Hailey Baldwin

Justin Bieber serenades Hailey Baldwin outside Buckingham Palace

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.

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.

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

Hailey Baldwin returns Justin Bieber's love

The 19-year-old model was first linked to Bieber in 2015 and the pair have remained silent on the allegations since, bar a few cuddly Instagram pictures. However, on Wednesday, Bieber said in a new interview that he "really love(s)" Baldwin, and now she has revealed she feels the same way.

"He's really funny. We have a good time together," Baldwin toldEntertainment Tonight.