Prince Harry has revealed he killed 25 people during his second tour of duty in Afghanistan as an Apache helicopter pilot.

The Telegraph – which obtained an advanced copy of the prince’s memoir, Spare – reported the Prince writes about six particular missions that resulted in “the taking of human lives”.

The Duke of Sussex said his kill tally was an act that left him neither proud nor ashamed, adding at the time it was simply his job as a soldier. He did not see his victims as “people” but rather “chess pieces” that had to be taken off the board.

“So my number is 25. It’s not a number that fills me with satisfaction, but nor does it embarrass me,” he writes.

Prince Harry at an observation post in Helmand Province, Afghanistan in 2008. Photo / John Stillwell, Pool, Anwar Hussein Collection, WireImage

The Prince goes on to note that the reason he has no guilt is because he remembers watching news coverage of the devastating 9/11 attacks and later meeting the families of the victims.

He said while completing his service he saw those responsible for the attacks and their sympathisers as “enemies of humanity”. Harry notes fighting against them was an act of vengeance after they completed one of the worst crimes in human history.

Harry, 38, first fought in Afghanistan from 2007 to 2008 as a forward air controller calling in air strikes.

He returned between 2012 to 2013 when he flew the attack helicopter.

• UK MP mocks Prince Harry's military service
• Doco bombshell: Markle 'existing, not living', Prince Harry wants to leave UK
• 'Knocked me to the floor': Prince Harry recounts attack by brother William in new book

Harry completed two tours in Afghanistan. Photo / Getty Images

The Telegraph reported Harry went on to note in the memoir that he saw the people he killed as “baddies eliminated before they could kill goodies”.

The now Californian-based royal said if he saw them as people it would not have been possible to kill them. The Army, he writes, “trained me to ‘other’ them, and they had trained me well”.

He said, “I made it my purpose, from day one, to never go to bed with any doubt whether I had done the right thing… whether I had shot at Taliban and only Taliban, without civilians in the vicinity. I wanted to return to Great Britain with all my limbs, but more than that I wanted to get home with my conscience intact.”

Writing about his time in the war-torn country, Harry noted that soldiers usually don’t know how many people they have killed. He only does because he watched footage from a nose-mounted video camera on his Apache helicopter.

The Prince said he is not ashamed nor proud of his kills. Photo / Getty Images

The camera recorded each mission in full.

Throughout the memior, Harry confidently writes the only shots he thought twice about were the ones he did not take. He then specifies shots that he should have taken to help his Gurkha “brothers” when they were under fire from the Tabliban.

One particular event the Prince recalls - according to the Telegraph - is when he was witness to a lorry attack by 30 Taliban but he was denied permission to fire on the enemy.

Harry served in the British Army for 10 years, achieving the rank of captain during that time.

Because of the Prince’s royal status and military status, his first tour of duty was cut short when foreign news organisations breached a news blackout that had been agreed with the British media.

When he returned for his second tour of service, the Taliban said they told its commanders in Helmand “to do whatever they can to eliminate him”.

Harry was withdrawn from the war early after an embargo agreement was broken by the foreign press. Photo / Getty Images

Because of his high profile, it’s understood the Prince continues to be a top target for terrorists and is part of the reason he took legal action over the Home Office’s decision to withdraw his full police protection for him and his family when they are in the UK.

His lawyer at the time said Harry “does not feel safe” because of this and is currently engaged in a legal battle to win back his security rights.