The Duke of Sussex said he felt "so ashamed" after wearing a Nazi uniform to a party, calling it "one of the biggest mistakes" of his life.
Harry caused outrage in 2005 when he donned the soldier's uniform complete with swastika for a fancy dress party.
The Duke addressed the incident during the third episode of Harry & Meghan, the explosive docuseries which aired on Netflix on Thursday morning.
Harry said: "It was probably one of the biggest mistakes of my life.
"I felt so ashamed afterwards. All I wanted to do was make it right."
He added: "I could've just ignored it and probably made the same mistakes over and over again in my life.
"But I learned from that."
Harry, who was 20 at the time, was pictured holding a drink and cigarette, while wearing the costume.
Clarence House issued a response saying Harry had apologised for any offence or embarrassment caused.
Harry was widely condemned in 2009 after being caught on film calling a former Army colleague "our little P--i friend".
The Duke's latest comments on the incident came as he discussed unconscious bias within the Royal family.
The third episode referenced when Princess Michael of Kent wore a Blackamoor-style brooch to an event the Duchess of Sussex attended in 2017.
Harry said: "In this family, sometimes you are part of the problem rather than part of the solution. There is a huge level of unconscious bias.
"The thing with unconscious bias, it is actually no one's fault. But once it has been pointed out, or identified within yourself you then need to make it right.
"It is education. It is awareness. It is a constant work in progress for everybody, including me."