Robert Downey Jr and Indio Falconer Downey spotted out shopping for clothes together at a Planet Blue store. [Photo/IC]

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Indio Falconer Downey, the 20-year-old son of the "Iron Man" actor, was arrested on Sunday afternoon with what authorities believe was cocaine and a pipe used to smoke it, Sergeant Dave Valentine said.

Valentine said Downey was arrested after the car he was a passenger in was pulled over by a deputy. No one else in the car was arrested.

Downey posted bail of $10,250 and was released shortly after midnight PDT (0700 GMT). He has a court date set for Aug 29.

Downey appeared in the 2005 crime comedy "Kiss Kiss Bang Bang" in which his father, who has also struggled with drug addiction in the past, starred alongside Val Kilmer.

Downey Jr said in a statement that he believes his son likely has genetic predisposition to addiction.

"There is a lot of family support and understanding, and we're all determined to rally behind him and help him become the man he's capable of being," Downey Jr said. "We're grateful to the Sheriff's department for their intervention and believe Indio can be another recovery success story instead of a cautionary tale."

He is Robert Downey Jr's only child with his first wife, Deborah Falconer. The pair were married from 1992 to 2004.