The singer, who recently split from Justin Bieber, spilled the beans during a chat with Ellen DeGeneres, telling the chat show queen she was nervous when she learned Brad was watching her performance of Come & Get it from the audience.
"I was so nervous. Like that stresses me out, but it was fine," Selena said. "I actually had fun and I got to meet Brad Pitt, so . . ."
When pressed by Ellen to reveal full details of their meeting Selena obliged. "Yeah, so I was in my dressing room and I had just finished performing.
"They knocked on my door and they said Brad Pitt would like to come in and I was like, 'He can come in.'
"I was trying to play cool and be really nice. As soon as he walked out I ran and I hide under the craft service table for like two minutes because I couldn't believe it was happening."
Despite her nerves, Selena was impressed by the father of Angelina Jolie's six children, and dreamily described him as being "so pretty".
Selena is hapilly single since splitting from Justin Bieber earlier this year. The starlet has worked her way through the break up, and is currently promoting her most recent film, Spring Breakers.
Her appearance at the MTV Movie Awards secured Selena with a sartorial hit as well as a professional one.
She lit up the red carpet in a fringed gold Julien Macdonald dress before belting out her new single Come & Get – which she insits isn't about her famous ex.
"Honestly, to be 100 per cent real, it's not really about a specific person," she told Ryan Seacrest.
"The reason why I wanted this to be the first single was because it exudes...confidence and strength and that is something I'm willing to share with the world."