The 61-year-old co-founder of Miramax Films says Stewart met the Prince at Madison Square Garden last December.
The meet-and-greet went off without a hitch and the unidentified man paid the money in cash.
Weinstein told the story at the Toronto Film Festival, where he's promoting 12.12.12 - a documentary about the Hurricane Sandy benefit concert.
Stewart was one of many celebrities who took part in the fundraiser in December. She gave a heartfelt speech about the hurricane, which caused massive damage to the New York and New Jersey coastlines.
"I am here to talk to you about New Jersey tonight,'' she said, before reading out a list of statistics about the disaster.
"Now is your chance to be Jersey strong with us,'' Stewart added.
Other high profile people who took part in the benefit included Bruce Springsteen, Adam Sandler, Susan Sarandon, Chris Rock, the Rolling Stones and Kanye West.
- Cover Media