Prince Harry is claimed to have shouted "what Meghan wants, she gets" at royal staff ahead of his wedding earlier this year.
According to royal biographer Robert Jobson, the Duke of Sussex was so "stressed" with wedding preparation that he became "petulant and short-tempered" with those around him.
As part of a serialization in the Daily Mail, the new biography "Charles at Seventy: Thoughts, Hopes and Dreams" claims that Harry would "raise his voice" to ensure Meghan Markle had her every wish met.
And although the Duke and Duchess of Sussex appeared relaxed and carefree on their Windsor wedding day, the royal expert writes: "The weeks leading up to the wedding had been far more tense for both Harry and Meghan than most people realized."
The couple is even reported to have booked a "series of appointments with Ross Barr, known as 'the acupuncturist to the stars'" as a means of coping with the stress.
However, the biographer claims "whether these treatments had much impact on Harry is debatable" as he continued to grow more short-tempered with royal staff in the weeks leading up to the wedding.
What's more, there were times where the pressure of the Royal Wedding (which was watched by over 1 billion people worldwide) appeared to get too much for the Prince.
Robert added: "Raising his voice on occasion, Harry would insist: 'What Meghan wants, she gets.'"
Describing Harry as "prone to volatility", the biographer revealed that "like this mother, he tends to wear his heart on his sleeve."
The new Prince Charles biography also explores his complex relationship with his sons and how both Prince Harry and Prince William take after Princess Diana.
Quoting a source close to the Palace, the biographer claims: "To this day, Charles admits he often finds it difficult to gauge either of his sons' occasionally unpredictable moods.
"In that aspect of their nature, both princes are very much like their mother."