Bradley Cooper's "biggest challenge" was keeping going through the long process of filming 'A Star Is Born'.

Bradley Cooper

Bradley Cooper

The 43-year-old actor co-wrote the script, directed and produced the movie as well as starring in it and he admits it was the "most fulfilling" movie he's ever been in.

He said: "It was most fulfilling I've ever been artistically. I guess the biggest challenge was just the fortitude to keep going because it was a long process and you can't really see the light at the end of the tunnel for a good half of that process. You sort of get up knowing you're gonna be digging a while before you find anything."

Meanwhile, Bradley's co-star Lady Gaga previously revealed he really "fought" for her to be in 'A Star Is Born'.

She said: "Can I just say - what an incredible filmmaker Bradley Cooper is. He's an incredible director, an incredible singer, an incredible musician and songwriter. I just feel so humbled to be here. I wouldn't be here without him. He really fought for me to be in this film. I'm really thankful to him."

And whilst Bradley doesn't think he would turn to singing as a career but is planning to record a song he wrote on set.

He added: "I don't even know how I would sing because I'm singing through him. He was a complete character. That said, there was one song that I wrote, called 'Too Far Gone' that I had the idea for a verse and a bridge, so I'm going to go to the recording studio and finish it. So I don't know what the answer is."