According to new legal docs, obtained by TMZ, the biological father of Anna's youngest daughter, Kylee, is suing Mama June for custody of Anna's 11-year-old daughter, Kaitlyn.
Michael Cardwell already took custody of 8-year-old Kylee, who he had with Anna, after her recent death ... and he says he's taken a parental role in Kaitlyn's life over the years despite not being her biological dad.
In the docs, Michael says Anna fostered and supported his relationship with Kaitlyn when Anna was still alive ... he says he behaved as though he were Kaitlyn's dad and claims Anna was on board with him continuing to spend time with Kaitlyn even after he and Anna separated. He also says he's paying for Kaitlyn's education.
Mama June tells TMZ … she hasn't been served with any legal papers yet but said she "can see him in court." The reality TV star says Kaitlyn wants to stay with her and her husband, Justin, and insists a change in custody "would be going against her wishes."
Michael claims Kaitlyn's biological father has never been involved in her life ... but Mama June says that means she should be the one to step into the parent role.
In the docs, Michael opens up some old family wounds, saying ... "Anna has had a very sorted [sic] relationship with her mother throughout her life and went various periods of time without speaking to her." He says Mama's presence in Kaitlyn's life has also been inconsistent.
But, Mama June's ripping the brewing custody battle, telling us ... "At the end of the day, the girls have lost their mother so why put them through this."