WATCH: Where did Barack Obama make surprise visit?

Former US president Barack Obama was spotted in 10 Downing Street during his unannounced visit to the United Kingdom where he met with Rishi Sunak, according to a Prime Minister spokesperson Monday.

Downing Street said that Obama was on an "informal courtesy drop-in" as he was visiting London. The visit marks the first time since the 62-year-old left the White House in 2019.

Obama waved toward photographers after meeting with Rishi Sunak, accompanying US ambassador Jane Hartley.

"He was making an informal courtesy drop-in as part of his trip to London, where he is conducting work of the Obama Foundation," the Prime Minister's official spokesman said.

He further said: "I think President Obama's team made contact and obviously the Prime Minister was very happy to meet with him and discuss the work of the Obama Foundation."

Obama paid a visit to the premier amid Sunak’s attempts to prevent the rebellion of the Conservative Party.

Earlier, the 43-year-old PM was asked about his call for the general election to which he laughed.

Last week, Sunak responded to a question regarding holding a general election on May 2, alongside the local elections. He said: "There won’t be a general election on that day."