"It was like maybe two years ago,' he revealed. "There'd just been a build up of stories, there'd been a build up of pressures.
"I couldn't fathom why there were people taking photos of me all the time. For me, it was like why are you doing this? I haven't done anything wrong.
"When your family's constantly being pursued and your name is constantly in the papers and online and in the magazines you feel like there's just no escape."
Karl says it took seeing several mental health professionals before he was diagnosed with PTSD.
He continued: "I'm able to cope with a great deal of pressure but pressure does build and if you don't look after it, it can sort of catch you unawares."
The TV star made a return to the Today show after he was famously axed from the Nine Network and is currently awaiting the arrival of his first child with Jasmine in May.
The popular television host also took the opportunity to urge people to seek help, especially with the strain the coronavirus pandemic is having on people's mental health.
"If something's not right then go and get some help. It's like going to the dentist, except less painful".