According to annulment documents obtained by TMZ, All-Star player Griner found out after they had tied the knot that throughout her engagement with Johnson, the latter was texting an ex-boyfriend.
The center for the Phoenix Mercury also claimed in the documents that she later found out that Johnson was still sleeping with a man - who may or may not be the ex-boyfriend - when they started dating last summer.
The 24-year-old also said that she wouldn't have proposed and married Johnson had she known of Johnson's affair with the said man.
She added that Johnson demanded, threatened and gave her an ultimatum and that's why she finally agreed to marriage and having a child with the forward for the Tulsa Shock.
The cheating allegations are quickly denied by Johnson's representative DJ Fisher, however, telling TMZ that Johnson is just popular and beautiful and that's why she has male friends. The Tulsa Shock player's rep added that such conclusion of infidelity could only be conjured by an insecure person.
The WNBA stars-turned-couple announced their split last month just one day after revealing that Johnson was pregnant.
After Griner filed an annulment on June 5, she gave a teary interview with ESPN in which she said she had made a 'huge mistake' and 'shouldn't have gone through with the wedding'.
Previously, the controversial Griner said she knew Johnson was straight, which was another reason why the All-Star player thought their relationship could end really bad.