Foster — who went through a nasty custody battle with the You Got It Bad singer — put her ex on blast in the comment section of Ye's post about which school his kids with Kardashian should attend.
The rapper made headlines when dropped a series of Instagram posts on Thursday night, insisting he hadn't come unhinged; he just wanted a say in their four children's lives.
One of Kanye's posts read, "I'm the kids father." In the caption, the Donda rapper tried to explain the situation. "Imagine not having any say so on where your kids go to school," he wrote.
That hit Foster hard and she couldn't wait to reply.
"Welcome to my world!" Usher's ex commented on Ye's post, adding several red exclamation marks to ensure it grabbed attention. Foster married Usher in August 2007, one month after suddenly canceling their pre-planned ceremony.
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She was pregnant with their first child at the time. Foster — who worked as a celebrity stylist before marrying Usher — gave birth to their first son, Usher “Cinco” Raymond V, in November 2007. Their second son Naviyd followed 13 months later.
The pair's marriage was short-lived. Usher filed for divorce in June 2009 after being separated for nearly one year.
He accused her of doing drugs in front of their sons. Usher also claimed she was an irresponsible mother. Foster had her own allegations about her ex-husband.
She claimed he was an absentee father who cared more about his career than spending time with the kids. Usher broke down when he addressed the bad dad allegations during their nasty custody battle.