During her 70 years on the throne, Queen Elizabeth saw a massive amount of change in the world, and with that, some great tragedies . She lived through World War II , major terrorist attacks and enormous social change, but when asked what the late Queen failed at during her reign, her former private secretary didn’t hesitate to tell royal biographer Gyles Brandreth his thoughts.

In his book Elizabeth: An Intimate Portrait , Brandreth wrote that he once asked the late Lord Charteris, who worked with Queen Elizabeth between 1950 and 1977, if the monarch had “ever felt she had put a foot wrong.”

“He said, immediately, ‘ Aberfan . She got that wrong and she knows it,’” Brandreth wrote. On October 21, 1966, a landslide of coal waste swept through the Welsh mining village of Aberfan, killing 116 children and 28 adults, most of them students and teachers at the local school.…