The star, who recently had a mass removed from his head after suffering a sudden migraine, revealed the news to fans on Instagram.
'So i have the news,' he wrote. 'It was a bit of a shock and i've got an interesting journey ahead and a bit of a battle.
'I am starting aggressive treatment for the next few months to fight the diagnosis of brain cancer. Please stay positive for me and ill try to update you guys on my progress.'
All our thoughts and prayers go out to Johnny at this difficult time.
This article first published on New Idea.