Robert Downey Jr. is ''proud'' of his son for voluntarily checking into rehab last month.

The 'Iron Man 3' star - who has battled with substance abuse in the past - is pleased Indio, 20, is seeking treatment to help curb is addiction to drugs.

A source told People magazine: ''Robert clearly understands the struggle, and while of course this relapse was very upsetting to him, he is very proud of his son. Indio truly wants to stay clean. And no matter what, his dad will be right there with him.''

Indio - whose mother is Robert's ex-wife Deborah Falconer - has managed to stay clean for a while, but fell off the straight and narrow last month.

The youngster was arrested for possession of cocaine in West Hollywood after police caught him smoking something out of a pipe in a car.

He was booked for possession of cocaine, but was released from jail a few hours later after posting $10,000 bail.

Robert, 49, released a statement the day after the arrest on June 29, claiming his son ''likely inherited'' his weakness for drugs, but will hopefully overcome it.

Meanwhile, 'The Avengers' star has other things on his mind now as he and his wife Susan Downey, who already have two-year-old son Exton together, are expecting a baby girl in November.