Ever since he was a teenager, Prince William has shared what can only be described as an "uneasy" relationship with his stepmother Camilla, Duchess of Cornwall.
After all, he was old enough to understand – and be drawn into – the tragic marriage breakdown between his parents, in which Princess Diana infamously described Prince Charles' mistress as the "third person in our marriage, so it was a bit crowded".
A source says 39-year-old Wills' frostiness toward Camilla "thawed somewhat" after she married his father in 2005, but they've never been best friends.
"Wills accepted that Camilla is who his father chose, and who he's always been in love with," says the insider. "But he always held her at arm's length, and she never tried to push him on that. William's at least been more warm than [Prince] Harry, who glowered at her in silence unless he was pushed into conversation."
But now, as the monarchy prepares to enter a new era, with 73-year-old Charles at the helm, things are going to change between the royal family's most senior members.
Woman's Day understands that after the Queen, 96, made it known via an unprecedented statement that Camilla had her full support to be known as Queen Consort when Charles accedes, the two future kings sat down for a father-son heart-to-heart.
"Charles knows Camilla faces an uphill battle to win the public's affection, and he needs Wills to lead from the front," says a source. "Charles asked William to be seen fully on board with her – and he wasn't sure if his son would agree to it."
But much to Charles' delight, William gave his backing.
"The Queen spoke privately with William about making Camilla Queen instead of Princess Consort, and he understood her logic," says a source.
"William accepts that it's time to let go of the past and look to the future for his family, and Camilla is a non-negotiable part of that. Besides, he's learned to admire her steadfastness and loyalty, and he's even begun to trust her."
William's backing couldn't have come at a better time for Camilla, 74, who is bracing herself for Prince Harry's memoir, due out later this year.
UK media reports suggest the 37-year-old runaway royal could lash out at his stepmother in these pages as a way of showing he disagrees with the palace decision to name her Queen.
"Camilla's feeling very anxious ahead of what could feasibly be a hatchet job for simply loving Harry's father," says a source.
"William's heart goes out to her, and he will be truly disgusted if Harry takes out all his emotions on her. No one knows yet what exactly will be in that book, but William has pledged to be there for Camilla if it gets as ugly – as they all suspect it might."