Just after Britain voted to leave the EU, Donald Trump described Brexit as a “beautiful, beautiful thing”.
Trump's victory in the 2016 presidential election shocked British diplomats in Washington and relations between PM May, a vicar's daughter, and Trump have been strained at times.
The enduring image of May's visit to the White House in January 2017, when she became the first foreign leader to meet the president after he took office, was Trump taking May's hand to help her down the steps of a White House colonnade.
He will arrive in the United Kingdom after a NATO summit in Brussels and shortly before a summit in Helsinki with Russian President Vladimir Putin.