Robert Downey Jr.'s eldest son is seeking treatment in rehab.

The 'Iron Man 3' star, who successfully battled his own drug addictions in the past, is reportedly very upset that his 20-year-old son, Indio, has become reliant on prescription drugs.

A source told the National Enquirer magazine: ''This is a nightmare for Robert because his boy has never been in trouble before. He's praying for Indio's recovery.''

Indio's mother, singer Deborah Falconer, who split from the actor in 2001 after nine years of marriage, confirmed their son is seeking help in a holistic treatment facility in Los Angeles but insisted his drug issues are not serious.

She said: ''He was not addicted. He was taking one pill a day.''

She added: ''We are hoping to do it the homeopathic way rather than with medications. He's being treated with vitamin supplements and organic foods. He's doing great. He'll be back playing music and doing better soon.''

A spokesperson for the 48-year-old actor declined to comment on the allegations.

Indo, who performs with his band The Seems, recently inked a record deal with Warner Bros. Records, according to MTV.com.

Earlier this year, Robert, who has been drug free since 2003, admitted he began using marijuana at the age of six, emulating his father, Robert Downey Sr., who was a frequent drug user.

He said: ''I wish I'd had proper discipline in my life at 18.''

Robert also has a one-year-old son, Exton Downey, with his current wife Susan Downey.