The actress taped a segment for DeGeneres' programme to promote new Snow White movie Mirror Mirror, and the presenter played her first joke before Roberts had even sat down for the chat.
She crouched outside the redhead's dressing room and jumped up at her as Roberts opened the door, prompting her to scream, ""Oh my God! Am I the perfect person to scare or what?""
Speaking about the incident on the show, set to air in the U.S. on Friday (23Mar12), the actress explains, ""It doesn't even come across how scared I was - it did not come across there and I changed (outfits) because I peed in my pants! I screamed like I was being mugged on a subway.""
Roberts also reveals she likes to play the same prank on her three children in their home: ""I realised I was getting too much joy from it, so I've had to tone it down. Just if I hear them coming and they don't know where I am in the house and I crouch down in their private space and they come in and I jump out. Little people can just catch air, they just vault (when they jump) - its so wrong!""
Later on in the interview, Roberts was given a taste of her own medicine when a man dressed as Snow White sneaked up on her - resulting in the actress screaming loudly.
Her cries turned into laughter as she declared, ""Thank God, I'm a jogger - I would have a heart attack. Who was it? That's a different Snow White!""