The `Twilight` hunk was left traumatised after a stunt went wrong during his first ever visit to the big top with his parents when he was a young boy.
The 24-year-old star told US TV show `The Today Show`: "The first time I went to the circus somebody died. One of the clowns died. His little car exploded. The joke car exploded on him. Seriously.
"Everybody ran out. It was terrifying. It`s the only time I`ve ever been to the circus."
Robert is not the only star who shuns the circus - P. Diddy and Johnny Depp both suffer from Coulrophobia, a fear of clowns. Diddy has a `no clowns` clause written into his contracts, and was once deemed unsuitable to appear on US TV show `Fear Factor` by a therapist because of his irrational phobia.
Speaking of his own fear, Johnny has said:
"There`s something about the painted face, the fake smile. There always seemed to be a darkness lurking just under the surface, a potential for real evil. Something must have happened when I was a kid."
Other celebrities with strange phobias include Billy Bob Thornton, who has a fear of antique furniture and Nicole Kidman, who has previously admitted to an irrational fear of butterflies.