However in time, the step siblings' relationship softened and Laura and William made amends.
“When they stopped blaming one another’s parents and let go of their painful pasts, Laura and William got along well,” Katie wrote.
Both William and Harry, as well as Will's then-girlfriend Kate Middleton, attended Laura's wedding to chartered accountant Harry Lopes in 2006, and their daughter Eliza Lopes was one of the flower girls at the Duke and Duchess of Cambridge's wedding.
Laura and Harry also have twin boys, Gus and Louis.
Meanwhile, Aussie audiences may recognise Camilla's son Tom Parker-Bowles from his days as a judge on Family Food Fight.
The food writer and father-of-two starred alongside Matt Moran and Anna Polyviou on Nine's cooking show for two seasons and shares daughter Lola and son Freddy with wife Sara Buys.
But even though his mother is a duchess and his godfather is Prince Charles, Tom does not feel connected to the royal family.
Speaking to Good Morning Britain on the subject of the royal family, Tom explained, “My mother married into it. She’s part of it. We’re the common children. We’re just on the side.”
Despite this, both Tom and Laura's positions could change when Charles becomes King.
According to a report by The Express, the Prince of Wales may bestow royal titles upon his stepchildren when he ascends to the throne.