Princess Diana 'Shoved' Stepmom Raine Down the Stairs After She Said She 'Felt Sorry' for Prince Charles Marrying Someone 'So Stupid,' Her Brother Claims

Princess Diana got into a physical confrontation with her stepmother, Raine Spencer, back in 1989.

The late Princess of Wales' brother, Charles Spencer, penned in his new memoir, Swan Song: My Sister, Diana, how the incident unfolded.

Diana and Raine — who married her father John Spencer in 1976 — had a tumultuous relationship throughout the years.

“The worst of Diana and Raine’s relationship took place long after childhood and tended to reach particularly low points around major family events,” Charles wrote.

He explained tensions came to a head during his wedding rehearsal dinner at the Spencer family home, Althorp.

According to the 9th Earl Spencer, 62, John's first wife and his mother, Frances Shand Kydd, was invited to the bash and Raine wasn't particularly nice to her.

Raine had instructed Frances — who was married to John from 1954 until 1969 — to sit in a different room than everyone else. This act reportedly infuriated Diana, leading her to “shove” her stepmom down the stairs.

Raine and Diana's verbal fight “unfurled at the top of Althorp’s main staircase,” Charles recalled, adding the socialite “went low” by making an eyebrow-raising comment to Lady Di.

Raine reportedly said to the princess: "I have always felt so very sorry for the Prince of Wales, [the then-Prince Charles], marrying somebody quite as stupid as you.”

Diana and the monarch, 77, tied the knot in 1981 and divorced in 1996.

“Diana paused for a second, surprised at the intensity of the spite. She then took a step forward, hooked a long leg round Raine’s calves before shoving her down the carpeted staircase,” Charles added.

“Raine fortunately landed flush on her buttocks, rather than on bone, and got up," he continued.

In an interview with People released earlier this month ahead of his memoir's publication, Charles noted Diana's staircase push was one of the three times in her life she "physically lashed out."

"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 [Diana] thought she was standing up for [Frances]," he looked back.

Charles went on: "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."