Christopher Andersen, author of The King: The Life of Charles III, writes that Prince Harry introduced his now-wife to Charles before taking their relationship public and the then-Prince of Wales thought she was "completely charming" and "absolutely delightful".
Andersen added that Charles thought Meghan was similar in appearance to Pippa Middleton, the Princess of Wales' younger sister.
Newsweek, who received an advanced copy of the book, reports that Charles didn't realise Meghan was mixed race with a Caucasian father and Black mother "until later".
"At the time, Prince Charles had no idea that Harry's new girlfriend was biracial," the book reads. "Not that it would have mattered at all, of course," Charles reportedly told a friend.
It's also alleged in the book that Charles once spoke to a woman of Guyanese descent and told her she "didn't look" like she came from Manchester.
It comes after Fox News reported that elsewhere in the book it claims Charles' former valet Michael Fawcett was in charge of putting toothpaste on the King's monogrammed toothbrush, as well as shaving his face and helping him with clothing and his shoes.
The valet's duties also extended to laying out the royal's pyjamas, while another former valet, Ken Stronach, was in charge of hand washing Charles' underwear and ensuring his beloved childhood teddy bear was by his side.
The author also alleged that Charles' former nanny Mabel Anderson, was brought out of retirement to mend the teddy bear, when the then-Prince was in his 40s.
"[She] was the only human being allowed to take needle and thread to [former] Prince Charles’ teddy bear," a former valet told Andersen, according to Page Six. "He was well into his 40s, and every time that teddy needed to be repaired, you would think it was his own child having major surgery."
Elsewhere in the book, it's claimed Charles has a very particular morning routine that involves having a breakfast tray that has to "contain a cup and saucer to the right with a silver spool pointing outward at an angle of five o'clock. Butter must come in three balls and be chilled. The royal toast is always on a silver rack, never on a plate. Assorted jams, jellies, marmalades and honey are served on a separate silver tray."
Never miss a thing. Sign up to Yahoo Lifestyle’s daily newsletter.
Or if you have a story idea, email us at firstname.lastname@example.org