The actor was filming the zombie thriller in and around Dorset when his security detail was approached by Tricia Wilson-Hughes, who was hosting an event to raise money for the neonatal care unit at nearby Princess Anne Hospital.
The gift shop worker was concerned the cast and crew's overwhelming presence would deter donors from turning out to the gig on Saturday (24Nov12), so she asked Pitt, who has six children with fiancee Angelina Jolie, if he could pitch in a few dollars.
And Wilson-Hughes admits she was awe-struck when the guard returned with an envelope of cash, telling BBC News, "He said, 'There's £700 in there!' I couldn't believe it, I was completely dumbstruck. He said if he had more he would have given it. I said, 'Honestly, that is more than enough, but if he wants to do anything in the future that is absolutely fine.'
"You hear negative stories about A-listers but I won't hear a wrong word against (Brad), I am in awe of him."