Prince Harry is good friends with Pippa Middleton

Prince Harry has been entertaining his comrades in Afghanistan by reading them extracts of Pippa Middleton's new party planning guide Celebrate.

Pippa, 29, sent Harry a copy of the book - which she's believed to have been paid £400,000 to compile - ahead of its release today.

'He couldn't resist reading chapters out loud,' says a source.

'It's raised morale and caused some much-needed cheer.'

Pippa and helicopter pilot Harry, 28, became friends after their siblings Kate Middleton and Prince William started dating at university.

Harry's army friends often joke about the pair getting together in the future and the £25 book arriving in the post gave them ample opportunity to tease the royal.

'Harry's the subject of lots of banter. Everyone winds him up about Pippa,' the insider tells The Sun.

'They take the mickey out of their friendship by calling her "wifey in the making". Harry loves a good joke, even if it's about him.'

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Anna Duff