Monday marked a milestone in the case of “affluenza” teen Ethan Couch, who turned 19 years old.

His case officially transferred from Tarrant County Juvenile Court to Criminal District Court. From now on, he's in the adult system.

Couch spent his 19th birthday in a solitary cell, where he's been for the last two months. His next appearance in court will be before District Judge Wayne Salvant, the same judge handling the case against his mother, Tonya Couch. She's waiting to learn if she'll be indicted for allegedly helping her son run off to Mexico.

Judge Salvant cut Tonya Couch's bond from $1 million to $75,000, but he put her under virtual house arrest, with a GPS monitor and weekly probation visits.

Judge Salvant will decide what conditions to place on Ethan Couch, and whether to give him an additional 120 days in jail.

But sooner or later, Couch will get a chance to continue the 10-year probated sentence he received in juvenile court for killing four people in a drunk driving crash when he was 16.

But there's a difference now: If he violates probation again, he could go to prison.

A hearing in adult court was originally set for April 18, but court officials said the date has not yet been determined.