For his role as a boxer in new movie Southpaw, Jake Gyllenhaal embarked on an incredibly gruelling regime

It barely seems a minute since Jake Gyllenhaal got super-skinny for his role in 2014 film Nightcrawler but now he’s embarked on an even MORE dramatic body transformation.

The 34-year-old actor majorly buffed up to play a boxer in new film Southpaw and embarked on a brutal training regime that saw him gain a whopping 15lbs worth of sheer muscle.

In fact Jake is almost unrecognisable as tough New York fighter Billy Hope in the flick.

‘I knew nothing about boxing when I started really,’ the heartthrob star admits.

‘I knew that in order for me to pull it off in any way, I was just going to have to learn how to do it.’

To transform his frame Jake worked VERY hard on his fitness. With the help of trainer and coach Terry Claybon, he trained for two three-hour sessions a day which included three hours of boxing followed by strength, conditioning and cardio work for the next three hours.

Oh, and both sessions had sit-ups thrown in too – OUCH. Jake got so buff that eventually he had built up to doing an incredible 2,000 of them a day.

In a new video clip of him filmed during training the actor confesses that he was keen to take on the daunting physical challenge.

‘When I set my mind to something I just won’t stop until I do it,’ he reveals.

‘It’s something I pride myself on. It’s something I hate about myself. By the end I felt like I could do it.’

Jake’s transformation is all the more startling given his previous weight loss for his role as journalist Louis Bloom in Nightcrawler.

The actor dropped over 20lbs for the flick in 2013 and shocked fans with his gaunt appearance.

All of this has left us wondering – just what will Jake to his body do next?!

Southpaw is set for release on 24 July.

Watch Jake Gyllenhaal get buff here…

The Affair’s Ruth Wilson: I understand the idea of wanting to escape a world that’s claustrophobic