Apparently, Amanda Bynes' recent DUI arrest was the tipping point for the troubled star, who has reportedly been showing signs of erratic behavior for the last few months.

On Sunday, the 28-year-old retired actress was arrested for DUI after she ran a red light and stopped her car in the middle of an intersection.

Although Bynes had a legitimate prescription for Adderall, California Highway Patrol officers said she was "out of it" and may have mixed it with "other drugs," reports TMZ.

However, before the arrest, Bynes had been reportedly expelled from the Fashion Institute of Design and Merchandising in Irvine.

According to Gossip Cop reports, the former child star repeatedly missed classes or would show up while she was high.

One FIDM student named Rachel told TMZ that Bynes wore sunglasses to class, laughed at inappropriate times and got into "horrendous arguments." Plus, she was "acting erratically."

Other students at the fashion school said that Bynes was caught cheating on a test and offered other students money if they agreed to do her homework for her.

Earlier this year, the "Hairspray" actress seemed to turn a new leaf after she left a luxury rehabilitation center and moved back in with her parents in Los Angeles. She managed to stay out of the headlines and seemed to be focusing on her physical fitness.

However, inside sources say that she was obsessed with her appearance and would spent the majority of her time at the gym examining her looks.

"It's very obvious that she is not 100 percent well," a source who saw Bynes at her Thousand Oaks gym over the summer tells People. "She is still obsessed with her body and spends more time in front of the mirror than she actually works out. She doesn't like when people look at her and has even confronted a few other members." 

Another insider told People that she did not like living under her parents' court-ordered conservatorship. 

"Her parents were closely monitoring her, including her driving," says the source of Bynes, adding, "She would have arguments with her dad in the car." 

According to her father, Rick Bynes, the starlet disappeared after the conservatorship ended in June, reports x17. 

"She's 28, she does what she wants," he said. "We don't know a thing."