London (CNN) US President Donald Trump has congratulated Boris Johnson on becoming the leader of the Conservative Party and the UK's next prime minister.

"Congratulations to Boris Johnson on becoming the new Prime Minister of the United Kingdom. He will be great!" Trump tweeted after Johnson won a landslide victory in a members' ballot against rival Jeremy Hunt.

Trump has often praised Johnson as a friend, and touted him as a potential prime minister even while Theresa May was in office. The two men also indicated a mutual willingness to work with each other should Johnson win the leadership contest.

Johnson will take over from May as prime minister after she steps down on Wednesday.

In an interview with CNN on Tuesday, Boris' father Stanley Johnson said he thinks his son will get along with Trump -- but warned that the relationship cannot be subservient.