Jason Reitman admits that making 'Ghostbusters: Afterlife' has been a "slow boil".

The 44-year-old director has helmed the latest movie in the supernatural comedy series and admits that he first came up with the concept several years ago, before he realised that it could explore the legacy of Dr. Egon Spengler – who was played by the late Harold Ramis.

Jason told HeyUGuys.com: "It was a slow boil. The character came to me about a decade ago and they floated around my head. I shared them with my friends as a joke before it became more serious.

"I then realised that it was the Spengler family and the story of the carrying on the family legacy echoed my own journey of taking on this 'Ghostbusters' legacy."

The 'Juno' director follows his father Ivan in directing a 'Ghostbusters' flick and admits that he often had to "pinch himself" on set, although he knew he was under pressure to deliver for fans of the franchise.

Jason explained: "I was pinching myself on a daily basis. It felt like I was making fan fiction but I was making another chapter of this story and was determined not to let everyone down.

"We had original equipment and music in storage so we dug into how 'Ghostbusters' was made to get this movie spot on."

Jason has worked closely with his father – who directed the first two 'Ghostbusters' films and is involved as a producer on the new flick – and was amazed by Ivan's passion for the film.

He said: "My father was the first person to read the script. He was on set almost every single day. He has watched the movie more times than me.

"My dad loves making movies and he loved being back in this mythology."