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Michael Jackson's father Joe has lashed out at the pop star's former dermatologist Dr. Arnold Klein for alleging his son was gay.

Klein's office manager Jason Pfeiffer appeared on U.S. TV news program "Extra" last week, claiming he had a sexual relationship with the late "Thriller" hitmaker.

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Klein echoed the allegations, telling Pfeiffer was "the love of [Jackson's] life". He also recalled walking in on the two men with their shirts off.

Klein admits he and Pfeiffer have been the target of "horrible death threats" since going public with the claims, which Joe Jackson calls "not true".

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And the patriarch has lashed out at Klein for breaking doctor/patient confidentiality. He adds, "Michael was not gay.

"[Klein] has no respect for Michael ... to say things about him when he's gone is shameful. He's a doctor and knows better than to break his vows against a patient."

Michael Jackson died last June 25, aged 50.

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