Stacey Flounders, who has a two-year-old daughter with Johnson, is said to be getting close to Bolton Wanderers striker Gary Madine, 26, who enjoyed a spell at Sheffield Wednesday.
According to The Mirror, she met the former Owls star in January, and believes he is a 'changed man' since he attacked two fans in nightclubs in 2013.
Sex offender Johnson is reportedly 'absolutely choked' at the news, as he had wanted to rebuild their relationship when he is released from Doncaster's Moorland Prison in two years.
'It's still early days, but Stacey really likes Gary. They're getting to know each other and Adam is aware of their relationship,' a source told the newspaper.
Madine was sentenced to 18 months in prison for punching two men in nightclubs.
The striker for Sheffield Wednesday punched fan Daniel Beresford in the Paris Bar in Sheffield in February 2013, breaking his nose.
Four weeks later, he punched Reece Hall, a bricklayer who supports rivals Sheffield United, in the Viper Room club and shattered his cheekbone.
He has a previous conviction for knocking out a man in a Carlisle pub.
This week Johnson was caught lying in prison about celebrities he's slept with the day after shocking footage emerged of him boasting about his vile crimes. He was jailed for six years in March for engaging in sexual activity with a besotted 15-year-old
"Adam is in pieces about Stacey's romance with Gary and his family are absolutely fuming because they thought she would stand by him,' an insider told The Sun.
"He's absolutely gutted. As far as he was concerned he was still with Stacey - so he feels like he has been betrayed."
Johnson's trial at Bradford Crown Court heard that he had kissed and sexually touched a teenage girl in his Range Rover, in a secluded spot in County Durham.