During their time as royals, Prince Harry and Meghan both shared the same funding pot from their father’s Duchess of Cornwall estate.
According to Andrew Morton, Prince William took priority over Meghan and Harry, prompting arguments and "jealousy” between the brothers.
Mr Morton wrote: "They [Harry and Meghan] were coming to appreciate that in the royal hierarchy, no matter how popular, inspiring or relevant they were to the outside world, they were low down on the royal totem pole.
"Both William and Harry were funded by their father and it was often the case that Harry's ambitions did not match Prince Charles's budget.
“His brother, as the future king, would always take priority.
"It may have been frustrating, it may have led to rows and jealousy, but that was the way it was and that was the way it was always going to be."
Clarence House, Kensington Palace and representatives for the Duke and Duchess of Sussex have been contacted for comment.
Additional reporting by Isabella Marsans, Francesca Edwards, Ewan Boyle and Steven Brown
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