"When I was a kid, I was lost," Montgomery wrote in an Instagram post Monday night that featured a childhood photo. "I had a really tough time in school. I was a big kid who loved drama...I never got passing grades, I wasn’t popular or a gifted sports player. Girls were never interested in me. I suffered from anxiety from a young age. I was distracted and I wasn’t focused. But I had a dream, I was lucky — I knew what I wanted to do. And every night I went home and I focused on THAT." He added: "I lost weight, I went to drama school and I never stopped wanting it, I never stopped being curious. I never let the failures get me down."