Prince Philip Once Said the Queen's "Abundant" Tolerance Was the Key to Their Successful Marriage

• Earlier this month, the world joined the royal family in mourning the death of Prince Philip, who died on April 9 at the age of 99.
• In his book Long Live the Queen! 13 Rules for Living from Britain's Longest Reigning Monarch, royal author Bryan Kozlowski shares that Philip once discussed the secret to his decades-long marriage to Queen Elizabeth II.
• When asked about his marriage to Elizabeth, which lasted for 73 years until his death, Philip said "tolerance is the one essential ingredient." He added that the Queen's incredible tolerance deserved credit for his and Elizabeth's marital bliss.

Prince Philip and Queen Elizabeth II were married for 73 years until his death earlier this month—and Philip knew exactly what made their union work.

In his book Long Live the Queen! 13 Rules for Living from Britain's Longest Reigning Monarch, royal author Bryan Kozlowski discusses the secret to Elizabeth and Philip's long and happy marriage and, it turns out, that secret was actually shared by Philip himself.

According to Kozlowski, Philip readily admitted that "tolerance is the one essential ingredient" when it came to maintaining a healthy and happy marriage with his wife, the.

In Philip and Elizabeth's union, it wasn't usually the notoriously temperamental Duke of Edinburgh who displayed tolerance though. "You can take it from me that the Queen has the quality of tolerance in abundance," he explained.

Kozlowski describes this as the Queen's ability to "strategically keep her distance in her own family"—a skill that he says benefitted Philip in particular over the years.

"He might be her 'strength and stay' of over seventy years, but he has also been irritating, testy, critical, grumbly, cruel and isn't shy of calling the Queen 'a bloody fool' when his dander is up," Kozlowski explains in the book, published before Philip's death. "During such moments, Elizabeth makes every effort to remove 'herself from the blistering line of fire,' says biographer Carolly Erickson. 'I'm simply not going to appear,' the Queen would say, 'until Philip is in a better temper.'"

The Queen's ability to recognize when Philip needed that space—and to tolerate the moodiness in the first place—was clearly an important component in their 73 years of wedded bliss. Our thoughts are with the Queen, and the rest of the royal family, as they mourn the loss of Philip.