Charles Spencer Reveals the Rare Moments Princess Diana 'Physically Lashed Out'

While Princess Diana's shy demeanor was known to be one of her most prominent qualities, her brother, Charles Spencer, recently revealed the rare times she "physically lashed out."

In a new interview shared ahead of the September 22 publication of his book, Swan Song: Diana, My Sister, Spencer, 62, opened up about the late Princess of Wales' personality.

The 9th Earl Spencer divulged to People there were just three separate times in her life that Diana showed off her hidden fiery side.

"I can only think of three moments where Diana physically lashed out," Spencer said. "One was slapping my father when he told her he was marrying my stepmother [Raine Spencer] because that was a huge shock to us all."

Diana — who died in 1997 at the age of 36 — famously had a rough relationship with Raine when she married John Spencer in 1976.

"We all have experience of step relations, I’m sure, but it can be very tricky and we felt we had made our feelings really clear, but of course my father had to follow his heart," Charles continued. "As children, you don’t understand that."

He further noted he thought his father was "letting" him and Diana "down" by remarrying. John was married to Diana and Charles' mother, Frances Shand Kydd, from 1954 until 1969.

Another instance where Diana got physical, was when she pushed Charles "off my bike for no reason."

"That could just be a sibling thing, but it was really bizarre actually because it was so out of the blue," the British peer stated.

The final moment of Diana's rage came when she apparently pushed Raine down the stairs at the Spencer ancestral home, Althorp, in 1989 after the two women had a heated argument over Frances during Charles' wedding rehearsal.

"I’m not saying it’s a good thing in any way to be physically violent, but it was the buildup of an enormous amount of really strong feelings and a flashpoint where I think she thought she was standing up for my mother," Charles noted to People.

"My stepmother allowed my mother into the house here, but had her taken to a separate room to everyone else so she couldn’t mix with everyone. And I think Diana thought that was so unbelievably rude," he recalled of the tense time.

He continued: "And then Raine was quite insulting to Diana and said she couldn’t believe that Prince Charles had married someone so stupid. So I think that was probably lighting the fuse. I’m not here to say anyone can be physically violent, but it didn’t have no reason."