Simon Pegg may have come a long way from starring on cult TV series Spaced, but the Star Trek and Mission: Impossible actor admits that being a part of these huge franchises hasn't made him happier.

Pegg rose to international fame largely for his roles as star and co-writer of Shaun of the Dead, which opened the door to a Hollywood blockbusters like Mission: Impossible III and the Star Trek reboot.

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Speaking with The Guardian about his battle with alcoholism and depression, Pegg admits he didn't believe he belonged alongside stars like Tom Cruise when he got his big break in Mission: Impossible III. He confessed that he thought, “Am I really here with all these famous people?” Continuing about his role in Mission: Impossible III and tenure in Star Trek, he said, “I would feel like – I’m in a film with Tom Cruise, I’ve got the part of Scotty in Star Trek. This should be making me feel happy,” he says. “But it wasn’t.”

Ricky Gervais was once due to play Benji Dunn in Mission: Impossible III before a shift in the production schedule forced him to drop out. Pegg was then cast as the IMF technician turned field agent, and will reprise that role for the upcoming Mission: Impossible - Fallout. Pegg's time on the set of Mission: Impossible III was afueled by alcohol, and is an experience he never wants to repeat.

“When I watch that film back, I can see where I was then, which was fairly lost, and unhappy, and an alcoholic," he revealed. Although Pegg has suffered from depression from the age of 18, he calls the early 2000s the "crisis years." The news may come as a revelation to the star's fans, but he told The Guardian, "I hid it. I’m an actor, so I acted … all the fucking time.”

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Thankfully, things soon got better and Pegg cites his time on Brad Bird's Mission: Impossible  - Ghost Protocol as a turning point. According to the actor, audiences can actually see him get healthier over the course of the movie.

These days, the 48-year-old actor has found enjoyment in movies like Ready Player One and even stuck in Easter egg cameos for Star Wars: The Force Awakens and The Cloverfield Paradox. With Mission: Impossible - Fallout tracking to have the biggest opening of the series to date, there is plenty for Pegg to smile about other than beating his own personal demons.

Also starring Rebecca Ferguson, Michelle Monaghan, Alec Baldwin, Sean Harris, Sian Brooke and Frederick Schmidt, Mission: Impossible — Fallout arrives in theaters July 27.