The author of the controversial new book on the Trump White House is predicting consequences if President Trump Donald John TrumpHR McMaster says president's policy to withdraw troops from Afghanistan is 'unwise' Cast of 'Parks and Rec' reunite for virtual town hall to address Wisconsin voters Biden says Trump should step down over coronavirus response MORE is not invited to the royal wedding later this year.

Michael Wolff said during an interview with the Daily Mail on Sunday that a post-Brexit U.K. trade deal with the U.S. could be at risk if Trump doesn't get an invite to Prince Harry and actress Meghan Markle's wedding.

"He doesn't like being snubbed and wants to be the center of attention all the time," Wolff said during the interview.

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"Trump's foreign policy doctrine is simple: you Brits suck up to him and enlist in whatever geopolitical fantasy he has going, he'll give you what you want — though only if it doesn't hurt him. It is not so much vengeance, rather 'you flatter me and I'll flatter you.' "

Wolff said Trump will "value the Brits" if they give him what he wants.

“He sees the queen in reality TV show terms. That’s the Trump modus operandi," he said. "He will try to Trumpalize the queen and Buckingham Palace.”

Wolff's book, "Fire and Fury: Inside the Trump White House," which was released last week, has spurred conversations about Trump's mental fitness for office.

British Prime Minister Theresa May was asked about accusations that Trump is mentally unfit to hold office and appeared to dismiss concerns.

“When I deal with President Trump, what I see is somebody who is committed to ensuring that he is taking decisions in the best interests of the United States,” she told the BBC.

Trump has blasted claims made in the book and defended his mental health, calling himself a "very stable genius."