Even the most casual royal fan knows that Princess Diana and Prince Charles' marriage was infamously troubled. The couple separated in 1992, but didn't divorce officially until four years later, in 1996.
Prince William was 10-years-old when his parents first split and their separation was hard on him—especially in the years leading up to their actual divorce.
In his new book, Battle of Brothers: William and Harry—The Inside Story of a Family in Tumult, royal biographer and historian Robert Lacey reveals the role Will's grandmother, Queen Elizabeth II, played in helping him through the difficult time.
"It was then three years after his parents’ separation—just two years before Diana’s death—and the Queen was worried about William’s state of mind," Lacey writes in the book, according to Us Weekly.
"The Queen actually feared that the boy might be heading for some sort of breakdown, she confided to one of her advisors—just as the prince’s mother herself had clearly cracked up mentally in several respects."
According to Lacey, Will's grandfather, Prince Philip, agreed that he needed extra support and even encouraged the Queen to try "to get closer to this particular boy—who was not just her fragile grandson, but a future inheritor of her crown."
The Queen's solution was simple, but perfect: She started a special routine of having lunch with William every Sunday.
Something Lacey says "helped to turn the fragile schoolboy heading for a breakdown into quite a tough young man" and helped give the young royal a "moral compass and a purpose."
This article originally appeared on Marie Claire U.S.