"She said it’s a very – and she’s right – it’s a very complex problem, I think nobody had any idea how complex that was going to be," Trump said.

"Everyone thought it was going to be ‘Oh, it’s simple, we join or don’t join, or let’s see what happens'."

The royal family famously do not express political views and do not vote – and world leaders do not typically reveal what was discussed in private meetings. Although the Queen did once wear a hat that some said looked like the EU flag for the state opening of the parliament session that would come to be dominated by Brexit.

Apparently after realising this, Trump switched back to discussing how "beautiful" he thought she was.

"Let me tell you what I can talk about...she is an incredible woman, she is so sharp, she is so beautiful, when I say beautiful – inside and out," he said. "That is a beautiful woman."

