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, however Buckingham Palace have yet to confirm whether this is the case.
May added, however, that despite the policy she would still welcome Trump for his visit to the United Kingdom next month.
A spokeswoman for Buckingham Palace declined to comment.
British Prime Minister Theresa May on Wednesday, June 21, said images from the United States of migrant children kept in cages were "deeply disturbing" and that she would press President Donald Trump on the issue.
The prime minister has been a frequent critic and the relationship between the two appears to have soured after May became the first world leader to visit Trump's White House last February.
Princess Charlotte is already ‘obsessed’ with fashion aged three, Prince William reveals
His next public appearance is likely to be his christening , for which no public date has been announced. Prince George was christened in the same location in 2013.
"Meeting Her Majesty is the most important thing because she's the head of state, and from then on, it'll be what the president wants to do", Johnson said.
Trump will touchdown in Britain on July 13 for a business trip. Britain's Stop Trump Coalition in London is already planning a protest for the president's upcoming visit.
File photos shows a video grab from footage broadcast by the UK Parliament's Parliamentary Recording Unit showing Britain's Prime Minister Theresa May.
In January, he canceled a planned trip to London to open the new US embassy, blaming his predecessor Barack Obama for what he called a bad deal on the embassy move, even though it was agreed in 2008 before Obama took office.
Elizabeth, 92, the oldest monarch in British history, has met 11 of the 12 US presidents before Trump who has been in office since she ascended the throne in 1952.