Big Tigger's Alleged Mistress Sues Estranged Wife for Defamation

The legal fallout from Big Tigger's domestic violence case is growing ... his longtime radio co-host, Francesca Amiker, is now suing his estranged wife.

According to court documents, obtained by TMZ, Amiker filed a defamation suit against Alicia Brown ... claiming she lied about her on social media by posting the Emmy Award-winning journalist had an affair with Big Tigger and helped destroy their marriage.

Amiker insists her relationship with the radio host has always been strictly professional and claims Brown's posts labeling her a "homewrecker" unleashed a wave of online hate, which damaged her reputation, cost her business opportunities, and forced her to hire a crisis management team. She's seeking unspecified damages.

The lawsuit comes as Big Tigger -- whose legal name is Darian Morgan -- continues to face domestic battery and child cruelty charges stemming from an alleged altercation in May with Brown at their Sandy Springs home.

As we've previously reported ... TMZ has since obtained Ring camera footage that investigators say shows Morgan approaching Brown from behind, grabbing her by the neck and struggling with her as she repeatedly yells for him to let go.

Police allege Brown was ultimately shoved into a door, suffering a deep cut above her left eye that required medical treatment and stitches.

Investigators also allege the couple's 13-year-old son was inside the home and able to hear the altercation, leading prosecutors to file the child cruelty charge.