Shocked By Amy Schumer

"I just had a gut instinct that she was a real storyteller," the 47-year-old recalls of listening to Schumer who appeared on the radio show as a guest. "Her act had a lot of great jokes, but not long stories, and when I heard her on Howard Stern, I thought, 'I don't think she realises how good a storyteller she is.'"

After meeting with the actress and encouraging her to write something for him to look at, Apatow was shocked at just how impressive her work was, given she'd never been involved in a feature film before.

"From the very beginning all of her writing was really strong and it was thrilling to get pages from her. She was very willing to write from a personal place; sometimes you ask people to do that and they refuse. She was really brutally frank and open and vulnerable right from the start and you have to do that to write well."

"[Amy] was very willing to write from a personal place; sometimes you ask people to do that and they refuse.

The new romantic comedy stars Schumer as the lead character — a commitment-phobic woman who falls for a sports doctor, played by popular comedian and Saturday Night Live alumnus, Bill Hader. While the actor is one of the best comedic talents going right now, this is the first film in which he plays a romantic lead rather than the outlandish, eccentric characters he was best known for on SNL. Initially, Apatow only called Hader in to read for the film, without any intention of casting him in the role. "I always wanted him to do it, but I wanted to make sure the chemistry with Amy was great. Bill and I had developed a movie for years; we never got it to a place where it was ready to shoot and I always wanted to find a project that would show off what he's like in real life; he's an incredibly charming, likeable, hilarious person and just as funny being subtle as playing broader characters.

"When Amy started writing this, in the back of my head, I thought, 'I think this could be the one for Bill Hader,' but I can't force that on Amy, I had to make sure she feels like there's chemistry and that this would be something special."

As well as the two strong leads and supporting roles from notable stars such as Colin Quinn and Vanessa Bayer, a special mention must be given to athletes WWE superstar John Cena and basketball living legend LeBron James, who also feature in the film.

Cena, who plays a sexually confused boyfriend of Amy, and James, the sensitive best friend to Hader's character, Aaron, arguably steal every scene in which they respectively feature, surprising even Apatow.

"I'm one of the few people that's found a way to make LeBron James more money"

"I thought they would be good, but I didn't know they were that good. John Cena really made me laugh. His audition was very, very funny and then we did a table read and he was even funnier… but then he just tore it down.

"LeBron completely blindsided us with how hysterical he was. He showed up and was just as loose and hilarious as anybody we work with."

With news that the Cleveland Cavaliers star has signed a film deal with Warner studios, rumours are rife that James is planning to star in a sequel to the 1996 comedy hit, Space Jam. It's fair to say Trainwreck is to thank for it. "I'm one of the few people that's found a way to make LeBron James more money," laughs Apatow.

Apatow's directorial work has very often featured stars who were on the rise. Carell's The 40-Year-Old Virgin came out in 2005 just as the Oscar-nominated actor began to receive international fame for his TV show, The Office, and Rogen, while a lead star in Apatow's 1999 series Freaks & Geeks, put his name on the map with 2007's Knocked Up. Schumer seems to be in that same field and while it isn't intentional, Apatow admits he does love working with fresh talent. "I just like helping people try to figure out how they can go to the next level; that's just interesting to me. It's especially interesting when they don't know at all how they would come across as a lead in a movie and it's fun to try and help people define their personae.

"It's also fun to work with people when they care so much — when you're trying to break through, you'll never care as much as that moment."

"It's also fun to work with people when they care so much — when you're trying to break through, you'll never care as much as that moment."

Meanwhile his latest book, Sick In The Head: Conversation About Life & Comedy, is an homage to his love of comedy, interviews the director has conducted with massive names like Jerry Seinfeld, Steve Martin, Chris Rock and more over some 30 years. As an aspiring teenage stand-up, Apatow felt the only way he could learn the tricks of the trade was by meeting and interviewing some of his biggest comedy heroes. His ambition resulted in his lying to publicists to obtain interviews, which included a visit to Jerry Seinfeld's New York apartment in 1983 — Apatow was still just 16 years old — and even a three-hour train ride to meet Weird Al Yankovic.

"I just so wanted to meet comedians that I was fearless due to my need to understand how comedy worked. I loved talking to them, I couldn't have been more excited. I just had to know what they knew."