'90 Day Fiancé' Thais Ramone’s Ex Claims She Slapped Him During Fight Over Kid

"90 Day Fiancé" star Thais Ramone allegedly slapped her estranged husband, Patrick Mendes, prompting her arrest for domestic battery .... TMZ has learned.

According to the police report, obtained by TMZ, Patrick called cops on May 22 and reported a domestic violence incident with Thais. He claimed she slapped him in the face at her Nevada home.

Once officers arrived, Patrick told cops he'd served Thais with divorce papers 2 days prior and went to her home that day to let their child say goodbye because Thais was leaving for Brazil, her native country.

Patrick claimed Thais became upset when he was in the home, and an argument erupted. He told cops Thais got physical during the argument, "Thais slapped him on the left side of his face with an open right hand.”

The officer said Patrick had marks on his face consistent with his story ... and Patrick had the slap on video.

During questioning, cops say Thais told them that Patrick was “controlling.” Cops say she acknowledged the fight but claimed she acted in self-defense.

Based on their investigation, police determined Thalia used force on Patrick ... and they arrested her at the scene for domestic battery.

As TMZ first reported, the D.A. ultimately determined they would not pursue criminal charges against Thais.

Thais and Patrick’s divorce remains pending.

Thais’ rep previously told TMZ, “Situations involving relationships and family dynamics are rarely black and white, and she has no interest in escalating negativity publicly.”