Carey Mulligan has spoken of her pride after her Army captain brother helped save a girls’ school that had been targeted by the Taliban.

Owain Mulligan was deployed to Afghanistan in 2012. While there he learnt how insurgents had deliberately poisoned a water source at a nearby school, forcing it to close.

The Great Gatsby actress revealed her older brother – at that time working as a linguist for the Army, mentoring Afghan forces – set about trying to raise money to create a new well.

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Charity work: Carey Mulligan was inspired to become an ambassador for War Child after her brother helped save a girls' school

In doing so, he contacted the charity War Child and as a result of his actions, the school later reopened.

Miss Mulligan, 29, said her brother’s efforts had inspired her to become an ambassador for the charity, which helps youngsters in war-stricken countries.

She told Harper’s Bazaar: ‘When my brother was a soldier in Afghanistan, he was at a base around the corner from a girls’ school that had to be shut down because of the Taliban. They had poisoned the water source. The only way it could reopen was if a new well was built. So my brother took up the initiative, amazingly, and started raising money for this school.’

She continued: ‘War Child was a charity that responded immediately. Since then, my brother has been a big fan, and when he left the Army… we met with them and started talking about working together… War Child is just extraordinary. They counsel kids through conflict and help them for years after a trauma.’

School saviour: The actress's soldier brother Owain Mulligan was based in Afghanistan as a linguist for the Army

Carey Mulligan features on the cover of the December issue of Harper's Bazaar, out tomorrow

Miss Mulligan, who is married to Mumford and Sons frontman Marcus Mumford, also works with the Alzheimer’s Society, after her grandmother was diagnosed with the disease.

Her brother’s military career began when he volunteered to serve with the Territorial Army in Iraq after graduating from Oxford University.

Miss Mulligan drew on the experience of having a sibling in the forces when she played Elsie, a character who objects to her brother going to war in ITV’s My Boy Jack.

According to previous reports Mr Mulligan, who is thought to be 30, spent some time with the Royal Artillery before commencing his degree in modern history.

While in the Army, he taught himself Dari and Pashto – the official languages of Afghanistan.

He reached the rank of captain before leaving the forces. He now works for a business consulting firm.

Miss Mulligan revealed her brother’s work in Afghanistan as she promoted her latest film, Suffragette, which also stars Meryl Streep.