Murray was sentenced yesterday to the maximum jail term after he was found guilty of involuntary manslaughter after giving Michael Jackson a lethal dose of the drug Propofol.

But Katherine said: Four years is not enough for someone’s son. It won’t bring him back but at least he got the maximum.”

The King of Pop’s family also released a statement saying: “As Michael’s parents, we never imagined we would live to witness his passing.

“There is no way to describe the loss of our beloved son, father and friend.”

Jackson’s brother Jermaine said he believes the doctor should have faced a more severe charge, for second-degree murder.

He said: “What happened yesterday was not justice. True justice shouldn’t feel as empty and pointless as this. Justice is not having some clown of a doctor act so criminally negligent with Michael’s life that he ends up killing him.”

He added that Murray should have been “charged with, and convicted of, second-degree murder and sent down for decades”.

Judge Michael Pastor, who sentenced Murray also ordered him to pay Jackson’s three children around $100 million (£64 million) for their father’s funeral and loss of earnings for the This Is It tour, which was due to take place after he died in June 2009.

The judge reportedly told the court: “There are those who feel Dr Murray is a saint. There are those who feel Dr Murray is the devil. He’s neither. He’s a human being. He stands convicted of the death of another human being.”

LA County officials said Murray will probably only serve two of the four years of his sentence.

Sheriff’s spokesman Steve Whitmore said the exact length was unconfirmed as yet but that under state law, non-violent criminals who are convicted in California usually only serve half of their sentences.