(CNN) Max Clifford, the UK's best-known celebrity publicist whose clients included OJ Simpson, has died at age 74, the UK's Ministry of Justice told CNN.

Nicknamed the "King of Spin," Clifford died in a hospital on Sunday after suffering a heart attack in prison. He was jailed for eight years in 2014 after being convicted of a series of indecent assaults on teenage girls.

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"As with all deaths in custody there will be an investigation by the independent Prisons and Probation Ombudsman. Our condolences are with Mr. Clifford's family at this difficult time," the ministry said in a statement. The cause of Clifford's death was "not self-inflicted" the statement said.

He was the first person to be convicted in an investigation into sex abuse allegations against the late British TV presenter Jimmy Savile.

Clifford denied 11 accusations of sex abuse dating from 1966 to 1985, calling his arrest and prosecution "a nightmare" and declaring his innocence.

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