William is ‘keeping quiet for the good of his family’, a royal source claims (Picture: Getty Images)

Prince William is said to be ‘burning’ with anger over claims made in Harry’s new memoir.

In extracts obtained by the Guardian newspaper, the duke claims he was physically attacked by his brother and knocked to the floor during a furious confrontation.

Harry also alleges that it was William and the Princess of Wales who encouraged him to wear a Nazi uniform to a fancy dress party 2005 and ‘howled’ with laughter when they saw it.

Spare comes out officially on Tuesday but was released early in Spain.

A close confidant of Williams claims the royal will ‘never retaliate’ despite how scandalous the content of his brother’s memoir may be.

The friend told The Times: ‘He won’t retaliate, he never would, because he’s dignified and unbelievably loyal. William is a sitting duck because Harry knows he isn’t going to retaliate. How many shots can you take at a sitting duck?

‘It’s cruel, cowardly and so sad for William to keep taking the punches. He’s keeping quiet for the good of his family and the country.

‘He’s handling it so well on the outside — inside he’s burning.’

The brothers’ tensions have reached new heights as Spare’s bombshells are dropped (Picture: Getty Images)

On Sunday, Harry: The Interview, which will be broadcast at 9pm on ITV1 and ITVX on Sunday.

Previewing his memoir, the duke will speak about his memories of meeting mourners outside Kensington Palace.

Diana, Princess of Wales died in a car crash when Prince Harry was just 12-years-old.

‘Everyone knows where they were and what they were doing the night my mother died,’ he tells presenter Tom Bradby in a preview clip.

‘I cried once, at the burial, and you know I go into detail about how strange it was and how actually there was some guilt that I felt, and I think William felt as well, by walking around the outside of Kensington Palace.

‘There were 50,000 bouquets of flowers to our mother and there we were shaking people’s hands, smiling.

‘I’ve seen the videos, right, I looked back over it all. And the wet hands that we were shaking, we couldn’t understand why their hands were wet, but it was all the tears that they were wiping away.’

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‘He’s keeping quiet for the good of his family and the country.’