The 28-year-old star said that his body transformation began in the Twilight saga, when he used the gym to escape from the attention he received during filming.
He said: ‘I was bored. They put us in these mall apartment complexes – the fans and paparazzi were outside the whole time. So I bunkered down in the gym; it was my escape.’
Being a vampire also meant going on a careful, calorie-controlled diet. ‘For Immortals, we all had dieticians: every hour they’d hand you eight almonds or a plate of spinach,’ he reveals.
He also explains he has a tactic of playing ignorant when he doesn’t like the menu.
‘Just ask if they have salmon and avocado and it they mind throwing together a salad for you. It’s being deliberately ignorant, but it works,’ he jokes.
And filming his latest role as Hercules, which involved swinging a 4kg sword, has put him in even better shape.
The film sees Hercules destined to fight his evil father King Amphitryon (Scott Adkins) who grows mad with power, conquering city-states and waging war.
‘Staying upright on a horse is hard on your abs, and swinging a sword really hits your core as well as your arms,’ Kellan reveals.