He replied: "Yes, yes, I mean he has to see the head of state".
Mr Trump was originally set to visit the United Kingdom in January to mark the opening of the new US Embassy in London.
Mrs May stated it was not the "British way" to treat migrants in the manner now being witnessed on the USA border, but she refused to cancel Mr Trump's planned visit to the United Kingdom next month.
"Meeting Her Majesty is the most important thing, because she is head of state".
"It's tragic and shocking to see innocent children caged like animals at United States migrant camps and to hear their cries of anguish after being forcibly separated from their parents", he wrote on Twitter, adding: "It's immoral and goes against fundamental human rights we must always respect, no matter the situation".
Speculation has been growing that Trump's visit would include meeting the Queen after it emerged Windsor Castle could be closed to the public on the day of his visit.
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Buckingham Palace declined to comment.
Sadiq Kahn today defended the right of residents to protest the president's visit.
The immigration policy was previously described by Tory MP Sam Gyimah as "indefensible".
Mr Trump is facing pressure from both sides of the political divide in Washington to end a "zero-tolerance" approach to illegal border crossings which requires adult migrants to be held in custody for prosecution, separated from their children.
Footage and photographs released by the department depict people, including children, housed in large metal chain-link cages within the administration's makeshift shelters.
Mr Trump blames Democrats for the family separations and said strict border rules are needed to keep criminals and gang members out of the US.