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Danielle Spencer -- famous for playing Dee Thomas on the hit ’70s sitcom "What’s Happening!!" -- has died at 60 following complications from cancer, TMZ has learned.

Her longtime friend and former costar Haywood Nelson -- AKA Dwayne from the sitcom -- tells TMZ Danielle passed away Monday night in a Richmond, Virginia hospital ... with her mom Cheryl and her jazz musician brother Jeremy Pelt by her side. Getty

Haywood says he was in Dallas when he got the heartbreaking call -- telling us he always saw Danielle as his little sis. The two last spoke just two weeks ago on the phone, and he says she sounded upbeat at the time.

Haywood adds Danielle had previously been in a car accident -- and was in a wheelchair.

He honored Danielle on IG Tuesday, saying her battle had tak

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