While filming scenes for his movie World War Z in the village of Lulworth in Dorset, England, the actor stumbled upon a mum's fundraiser and dipped into his own pockets to donate £700 ($1,075) to the cause - as well as getting the crew to chip in an additional £40 ($62).

If that wasn't generous enough, the 48-year-old heartthrob also promised to send a further donation once back in Hollywood, as a contribution from the rest of the crew.

Organiser Karley Gallagher was raising money for the neo-natal hospital unit that treated her sick son Zachary, who was born with gastroschisis, a type of hernia where the intestines stick outside the body.

But when she heard Brad Pitt was filming elsewhere in the village, she was convinced not a soul would show up to her event as they’d all be too busy star-spotting.

So her friend Tricia Wilson-Hughes, who was helping organise the fundraiser, put the message out to Brad’s people that a charity event was happening close by.

"I asked the security guards if Brad would be kind enough to make a small donation. They then came back with a brown envelope... We couldn't believe it, we were completely in awe," says Tricia.

"What he did for us was just incredible," adds a star-struck Karley. "It was a very generous and sympathetic gesture from him. I was grinning from ear to ear."

Brad, renowned for his philanthropy, has founded a number of organisations with fiancée Angelina Jolie to aid humanitarian causes around the world.

In 2009 the Jolie-Pitt Foundation donated $1 million to the UN and the following year a further $1 million to Doctors Without Borders, an organisation that helped provide emergency medical assistance to victims of the Haiti earthquake.