He may have been a boxing world champion and unbeaten in the ring, but Joe Calzaghe was still picked on when he was at school.
He told Newsround his story:
"I'm a champion boxer, undefeated, but I was bullied at school.
It was while I was boxing. I was British champion at the time but it didn't stop people picking on me, bullying me.
Kids on bikes would come to my house after school - they just wanted to pick a fight with me.
It was the start of a bad few years for me and the people who I thought were my friends suddenly weren't my friends.
They singled me out and started trouble with me.
It affected my lessons at school. I struggled with English and maths because I was so worried about being picked on in class.
I couldn't concentrate. It was a horrible situation to be in.
I overcame it with my boxing - if it wasn't for that I don't know what would have happened.
After school I would work out and focus on something else. That's what helped me."