Donald Trump's state visit to the UK: live updates - CNN

The Lofgran and Weed families outside Buckingham Palace. CNN

Crowds are beginning to gather outside Buckingham Palace ahead of US President Donald Trump's arrival to meet the Queen.

For two American families, Trump's UK trip came as a surprise. "We were on holiday and just read he was coming, and thought, 'this is going to be interesting!'” Andrea Lofgran, from Arizona, told CNN.

“When we came around the corner and saw the American flag and the Union Jacks together coming down the Mall it sent chills up and down. It was really special," added Lofgran, who is visiting London with her daughter Lauren, nine, and their neighbors Dave and Julia Weed.

“It’s pretty impressive if you think of the Queen and how many presidents she has met. That’s what blows me away," she said.

The Queen has met every US president during her reign, with the exception of Lyndon Johnson. Her first presidential meeting was with Harry Truman in 1951, a year before she ascended to the throne.

"I'm excited to see Marine One and the helicopters," added Lauren.

Joseph Afrane, 55, from London, is used to setting up camp outside Buckingham Palace. The royal fan was in place bright and early. -- wearing a specially-made suit -- as he has been several times for big royal occasions.

"If Her Majesty is holding a very important national event, I will come down as early as half past seven,” he told CNN.

Afrane said he was “very, very excited" about the US President's state visit.