Kelly and Jack Osbourne have become international stars

Jack Osbourne - the son of rocker Ozzy Osbourne - is in "good spirits" after admitting himself into a drug and alcohol rehabilitation clinic, his sister has said.

Kelly Osbourne added that she and her family had had no idea how serious her 17-year-old brother's problems were before he checked into the clinic last week.

Jack Osbourne's drug and alcohol problems became public in an interview with People magazine, published at the start of the week.

The Osbourne family have become the focus of media attention following the global success of their fly-on-the-wall TV show about the goings-on in their everyday life.

Kelly Osbourne, 18, has also begun a career as a rock singer while her father continues to perform. Jack Osbourne is a part-time talent scout for Epic Records.

In an interview with US Weekly magazine, Kelly Osbourne said the family had all been so busy they had not been together much recently.

Sharon Osbourne is her husband's manager

"I was on tour, Mum was working on her TV show, and Dad's in rehearsal," she said.

Jack Osbourne finally told his mother Sharon about his alcohol and marijuana abuse, she added.

"He sat with Mum and she said, 'We'll get you help, we'll figure it out'.

"He's doing very well and we're all very proud of him. He's in really good spirits."

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Jack Osbourne entered Las Encinas Hospital in Pasadena on 23 April.

He told People magazine: "I got caught up in my new lifestyle and got carried away with drugs and alcohol.

"Once I realised this, I voluntarily checked myself into a detox facility for my own health and well-being."

His father has had well-documented problems with substance abuse and recently turned to alcohol again when his wife was diagnosed with cancer.

Sharon Osbourne has reportedly said she blames herself for her son's problems after allowing him to appear in the family's reality TV show.

She has told the ABC network that the second 10-episode series of The Osbournes would be the last.

The show, she said, which drew record ratings for MTV this spring, had changed her family "so much".

Her children, she said, now had lawyers and business managers.

The first series was a big hit around the world but ratings tumbled in its second season.