She travelled from her home in Wilmslow, Cheshire, to Carrington House, a boutique hotel in Norfolk.
Kerry was supposed to get in trim after piling on 2st since having £15,000 worth of liposuction and plastic surgery the previous year.
But gruelling exercise was the last thing on Kerry's mind once she clapped eyes on her hunky instructor Steve Lockton, a navy fitness trainer who has a partner and a child.
'Kerry instantly bonded with Steve,' one source tells Now. 'He says they had a connection because of their similar backgrounds - he's a working-class, northern lad from Hull.
'Steve says she was a right laugh, but things spiralled out of control, especially after the first night.'
This was when Kerry, Steve, fellow instructor Scott Partis and a couple of others at the camp sat up until 5am boozing, but Steve and Kerry kept disappearing off.
When Steve's girlfriend of six years, Ayeshea Amihere, 30, tried to get hold of him the next morning, his phone rang out.
A pal tells Now: 'When she finally spoke to him, he admitted to drinking with Kerry, which she thought was weird at a boot camp. Then someone at the hotel phoned Ayeshea to say she suspected something was happening between Steve and Kerry and felt concerned.'
Ayeshea couldn't quiz Steve until he got home from boot camp four days later. According to the pal, she asked him directly if they'd slept together.
'He couldn't even look her in the eye. He couldn't say anything. It was then that she knew something had gone on - of course they'd had sex,' says our source.
Steve admitted to Now that he was with Kerry on boot camp, but when asked if he'd been intimate with her he responded: 'No comment.'
When that romance fizzled out, at a second boot camp this January, Kerry was accused of chasing married father of three Kevin Green, also a personal fitness instructor.
The fallout is still ongoing, with Kevin's wife battling to keep her man.
Kerry and Kevin deny that anything happened.
In a bizarre coincidence, Steve and Kevin are close friends who live in the same block of military flats in Eastney, Portsmouth, and work at a nearby naval base.
Where to next?
- 12 reasons people cheat
- Kerry Katona's weight loss
- Peter Andre in pics