'One Of The Biggest Mistakes Of My Life': Prince Harry Accuses William & Kate Of Advising Him To Wear Nazi Costume For 'Native & Colonial'-Themed Party

Prince Harry claimed his brother, Prince William, and sister-in-law, Kate Middleton, told him to wear the Nazi costume which put him at the center of controversy back in 2005, revealing he was deciding between that uniform and a pilot costume.

RadarOnline.com has learned the Duke of Sussex made the shocking revelation in his explosive memoir, Spare, in which Harry promised readers "raw, unflinching honesty."

One chapter detailed how William and Kate had allegedly shared their input on Harry wearing the uniform leading up to the "Native and Colonial"-themed party.

"I phoned Willy and Kate, asked what they thought. Nazi uniform, they said," Harry wrote. "They both howled. Worse than Willy's leotard outfit! Way more ridiculous! Which, again, was the point."

More than 250 guests were taken by surprise when King Charles III's youngest son showed up to the event dressed as a Nazi soldier with a red armband emblazoned with a big swastika, emulating a member of General Erwin Rommel's Afrika Korps.

Harry was only 20 when the images of him were splashed on the front page of The Sun newspaper, leading him to make a public apology due to the outcry.

"I am very sorry if I have caused any offense or embarrassment to anyone. It was a poor choice of costume and I apologize," he said at the time.

In hindsight, Harry recalled the gaffe as one of the "biggest mistakes of my life."

"I felt so ashamed afterwards," he shared in his memoir.

"'All I wanted to do was make it right," Harry continued. "I sat down and spoke to the chief rabbi in London, which had a profound impact on me."

"I went to Berlin and spoke to a Holocaust survivor," he added. "I could have got on and ignored it and made the same mistakes over and over in my life but I learnt from that."

Harry's costume claims are among many bombshell revelations within the pages, some of which were leaked prior to its official release on January 10.

The royal left no stone unturned in his memoir, detailing his strained relationship with William, past drama with Kate and his wife, Meghan Markle, and so much more.

As we previously reported, insiders said that King Charles III is "shutting out" Harry due to the January release. The pair had been attempting to work out their differences but the memoir only furthered the divide.

"Harry had an inkling his dad would leave him out in the cold when he became King," said another insider. "So, it has come as no surprise that discussions are taking place to have him pushed out."