The President and Mayor's history of trading blows can be traced back to 2015, when Khan reacted to Trump's plan for a 'Muslim ban'.
In December 2015, he said in a BBC interview he hoped Trump would lose the presidential election 'badly'.
Roughly five months later, when Khan was elected mayor in May 2016, Trump laid on some unusual praise: 'If he does a great job, frankly that would be a terrific thing.'
In comments reported by the New York Times, the future president also hinted Khan, a Muslim, would be 'exempt' from the proposed ban.
But days later the relationship soured after Trump admitted he was 'offended' by Khan's comment that his views of Islam were 'ignorant'.
The Mayor of London gave his consent for a giant baby Trump blimp to be flown over London
'When he won I wished him well,' Trump told Good Morning Britain. 'Now, I don't care about him. It doesn't make any difference to me about him.'
The feud intensified in the aftermath of the London Bridge attacks in June 2017, when a controversial tweet by Trump opened him up to widespread criticism.
'At least 7 dead and 48 wounded in terror attack and Mayor of London says there is 'no reason to be alarmed!', the president wrote.
Khan's spokesman released a scathing rebuke, pointing out the comment was taken out of context.
The mayor had 'more important things to do than respond to Donald Trump's ill-informed tweet', he said.
The US president and mayor of London's history of trading blows can be traced back to 2015, when Khan reacted to Trump's plan for a 'Muslim ban' during his presidential campaign
Trump didn't stop there - he again responded: 'Pathetic
