Scroll through the gallery to see all the times Bieber and Baldwin took fashion harmony to the next level.
The singer, clad in an oversized tie-dyed hoodie and black shorts, perched himself on the Queen Victoria Memorial fountain outside the Palace and began strumming his guitar.
"Well, they went off and got married", Baldwin said, adding, "I don't know what the deal is". Baldwin watched with fans and proudly filmed on her phone.
Meanwhile, it was recently claimed that Hailey and Justin, 24, have already tied the knot after they were spotted at the Marriage Bureau at the courthouse in New York City last week. It all started when the two were spotted at the Marriage Bureau at a courthouse in NY.
The rumours of the couple's marriage come two months after the pair got engaged in the Bahamas.
Still, People has reported this week that Bieber and Baldwin are legally married, as of last Thursday, but are planning a larger ceremony with family and friends for a later date. The model was announced as the first ever "style creator" for Adidas and sportswear company JD back in July. During the performance he said, pointing to Baldwin, it is "the love of his life".
An unnamed source told the magazine that the couple "didn't want anyone but their families to know they got married".