Mr Brandreth said he didn’t believe the Queen would bestow such an honour until at least their 10th wedding anniversary, due to the existing precedent.
He wrote: “In 2011, when Prince William married Catherine Middleton, the press talked up the possibility that the Queen might make her grandson’s bride a princess on her wedding day.
“It did not happen – and, so long as the Queen is Queen, I do not believe it will until William and Catherine have been married for ten years.
“The Queen always uses the honours at her disposal carefully and to a purpose.
“On Prince Philip’s ninetieth birthday, for example, she found for her husband a unique honour that was singularly appropriate.”
Mr Brandreth further discusses the possibility of Kate becoming a Princess in an exclusive interview with Express.co.uk.
While he didn’t think the title would be a wedding present, the royal expert believed it was still on the cards.
“I was sure she would not make Catherine a Princess in less than in the time that she made her own husband.
“So I felt the earliest date that was possible was the 10th wedding anniversary.
“But I don’t think we will find it is a 10th wedding anniversary present.
When asked, if it will come after this, Mr Brandreth said it will be in the “fullness of time”.
The royal biographer, who was a friend of Prince Philip’s, said in many ways it wouldn’t matter if Kate became a Princess or not, as she will inevitably become the Queen.
He said: “In a sense in some ways it doesn’t really need to in the case of Catherine because in the fullness of time she will become Queen.
“Camilla is Queen first then we will Catherine as Queen.
“It was more applicable to Prince Philip.”
A spokeswoman from Buckingham Palace told Express.co.uk: “This isn’t something we would comment on.”
Philip: The Final Portrait by Gyles Brandreth is available to buy now.