Princess Diana's younger brother Charles Spencer is revealing sexual abuse he suffered at a U.K. boarding school.

In a preview for an interview with NBC News correspondent Cynthia McFadden, Spencer opened up about the harrowing ordeal during a promotional appearance for his upcoming memoir, "A Very Private School."

The British podcaster and author said he was "sexually abused by a woman when I was a child."

"We were locked away, we were like prisoners," Spencer told McFadden. "We were prey to very bad people's worst instincts."

Spencer also told McFadden he first shared the abuse to a "therapist when I was about 42" after the therapist asked Spencer to whisper one thing he had "never told anyone."

What Diana's brother said at her funeralthat shocked many and delighted millions

In a statement, the prestigious school attended by Spencer, Maidwell Hall, told the "Today" show that it has notified local authorities to investigate possible crimes against children and also encouraged victims to come forward.

The full interview featuring Spencer and McFadden will air Monday on "Today."

Spencer is often remembered for his stirring speech at Princess Diana's 1997 funeral in Westminster Abbey.

"I would like to end by thanking God for the small mercies he has shown us at this dreadful time. For taking Diana at her most beautiful and radiant and when she had joy in her private life. Above all we give thanks for the life of a woman I am so proud to be able to call my sister, the unique, the complex, the extraordinary and irreplaceable Diana whose beauty, both internal and external, will never be extinguished from our minds," he said at the speech's end.

In recent years, he honored his late sister on what would have been her 60th birthday during a ceremony in 2021 at Kensington Palace in London, which included a sculpture unveiling. He also co-hosts a podcasts, "The Rabbit Hole Detectives."

Amid news of the sexual abuse revelation, Spencer took to Instagram on Friday to share a candid family photo from his childhood, featuring Princess Diana.

"I'm not sure I'm being entirely helpful, in this family shot from 1966, but I'm sharing it because I think it's the only shot I have of my parents, my sisters and me together; mainly because it was usually my father behind the lens," he wrote. "A happy moment at my childhood home - Park House, Sandringham - from long ago."

If you or someone you know is a victim of child abuse, call the Childhelp National Child Abuse Hotline at 1-800-4-A-Child or 1-800-422-4453, or go to www.childhelp.org.