Princess Margaret was Queen Elizabeth's rock, says royal biographer

Princess Margaret had a complex relationship with Queen Elizabeth, however both secretly supported each other through the tough times. 

Andrew Morton, who penned Elizabeth & Margaret: the Intimate World of the Windsor Sisters, explained the relationship between the royal princesses in this week's edition of PEOPLE magazine. 

Margaret "was someone who understood the Queen in a way no one else could," he said.

"They knew each other intimately from the day they were born. There is a unique intimacy between two siblings brought up together, brought up royal together, that is absolutely fascinating," Morton shared. 

"The parallels between William and Harry and Elizabeth and Margaret are there to be seen," he further revealed.

"In both cases you have one sibling who pushes boundaries," said Morton, "while the other is more cautious."

"Harry is being far more proactive in using his name and popularity to advance causes in a way Margaret never did," the author shared. "She much preferred to be carousing until 4 in the morning."