Donald Trump has begun his three day trip to the UK with an attack on London's Mayor - calling him a "stone cold loser".
Sadiq Khan said the US President shouldn't be honoured with a state visit, describing him as a "growing global threat" - which prompted a furious reaction from him.
A spokesperson for Sadiq Khan has described Donald Trump's tweet as a "childish" insult.
Air Force One landed at Stansted Airport in Essex this morning, where Mr Trump was greeted by UK Foreign Secretary Jeremy Hunt.
Hunt says he is a very controversial president who we've gotten used to over the last few years, and he expects the unexpected from the American leader.
During his trip the US President will meet the Royal Family, and discuss trade with Theresa May.
He will meet Theresa May tomorrow before travelling to Ireland to visit his golf club in Doonbeg in Co.Clare on Wednesday.