"One of the things I was really keen to trying to get to the bottom of in the book was how the Queen really felt about Meghan," Nicholl explained. "Because when you look at Meghan on paper she is not necessarily what you might expect of a conventional royal fiancé and that she's American, she's a well-known face."
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"She's filmed some pretty racy sex scenes that we've all seen in Suits. Everything from being a divorcee to being a bit older then Prince Harry, to coming from a dual heritage family, you might wonder if the Queen being of a certain generation and, of course, being the queen might have been at all concerned," she continued. "But everything I heard from the sources I spoke to was that she really felt from the outset that Meghan was a positive person in Prince Harry's life. That she made him very happy and that she was really very supportive."
Last week, the Queen officially gave her "most dearly beloved grandson" and his fiancée consent to marry. Though, the official letter made headlines after people noticed that the Queen simply referred to Meghan by her legal name, Rachel Meghan Markle. Meanwhile, in her consent to Prince William and Kate Middleton in 2011, she referred to the couple as "Our Most Dearly Beloved Grandson Prince William Arthur Philip Louis of Wales, K.G. and Our Trusty and Well-beloved Catherine Elizabeth Middleton.''
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But the Queen and Harry have always had a very special bond, and she will have a "very prominent and important role" in his wedding.
"I'm told from my sources at Windsor Castle that [Queen Elizabeth] is being very, very accommodating," Nicholl shared. "She has said to the couple, 'This is your wedding, this is your day. Plan it as you want it.' [This] is very generous because, don't forget, the queen is opening up her home."
"Don't forget she's hugely close to her grandson. They have a very special relationship. She is thrilled to be seeing Harry settle down and finally marry," she explained. "She's going to want to be a very important part of that day and indeed she will. But I think when it comes to the evening reception and certainly the party, if the Spice Girls are performing then, I don't think the queen's going to be on the dance floor."
See more on the upcoming nuptials in the video below, and keep up with all of ET's coverage on the Royal Wedding right here as we count down to May 19!