Tony Gilroy knows his way around a film set. But even Gilroy, the screenwriter behind “The Bourne Identity,” “The Bourne Supremacy” and “The Bourne Ultimatum,” was surprised by how challenging it can be to direct a movie.

“Directing is a lot more tiring,” said Gilroy, who directed and co-wrote “The Bourne Legacy,” the fourth instalment in the popular action series.

“When you’re writing a script you’re sitting in your office. But this was a couple of years running around the planet. It was a little different,” Gilroy said on Friday from New York on CTV’s Canada AM.

The 55-year-old American filmmaker travelled from the Philippines to Seoul, South Korea and Alberta to shoot scenes for this tale loosely based on the novel written by Eric Van Lustbader.

The search for a star to replace Matt Damon was also a long haul, according to Gilroy.

“We had a pretty extensive public search for a long time,” said Gilroy.

Damon played the character of Jason Bourne in the three previous franchise films. Indeed, for many fans Damon had become Bourne and played a significant role in the earlier films’ success at the box office.

However, treating “The Bourne Legacy” as a spin-off rather than a continuation of the franchise gave Gilroy the opportunity to introduce a new action man into the series.

In this instalment, troubled agent Aaron Cross takes audiences on a wild rollercoaster ride, jumping from trees, scaling walls and racing for his life on a motorcycle in breathtaking fashion. That rush is entirely attributed to 41-year-old American actor, Jeremy Renner, who did most of own stunts for this movie.

“Jeremy wasn’t available for a long time,” said Gilroy.

Yet unexpectedly, the actor’s schedule freed up and Gilroy pounced on the opportunity.

Gilroy also introduced the new character of Marta Shearling, played by Rachel Weisz, to this film as an unexpected and challenging ally for Renner’s character.

Both actors brought a level of skill and integrity to their roles that pleased Gilroy.

“The main theme here is authenticity,” said Gilroy.

“There’s a lot of mythology about Jason Bourne worked into the film for old fans. But even if you’ve know nothing about what happened before, you can still watch this movie and enjoy it. It will still feel real to audience,” he said.