IT’s all over for Donny and Marie!

After more than 35 years of showbiz stardom, the legend­ary brother-sister act may be finished for good.

Sources say a shocking medical crisis and bitter feuding are ripping the Osmond duo apart – and The ENQUIRER has all the stunning details.

The two began fighting like cats and dogs after Marie flipped out over the cancellation of her Hall­mark Channel talk show, insiders say. Now Donny faces a grueling six-month recovery from surgery to repair muscle damage. He suf­fered the agonizing injury when he landed hard on his behind during their Las Vegas act, and family in­siders fear he’ll never be able to sing and dance like he did before hurting himself.

“Marie tried to put a funny spin on her brother’s injury, joking, ‘I’ve always known Donny’s a butt, but now he’s proven it,’” a source told The ENQUIRER.

“But Donny’s injury was very serious, and it may spell the end for the Donny and Marie show in Las Vegas.”

Donny, 55, tore his gluteus maximus muscle while making a running leap onto a piano during their Sin City show at the Flamingo.

“The pain in Donny’s back and legs was so severe that doctors advised him to undergo surgery immediately,” said the source.

“Now, he’s extremely weak and has difficulty moving. He’s on anti-inflammatory medication and (the morphine-derived pain drug) Dilaudid. His doctors say he’ll need at least three months to heal, and then physical therapy to rebuild his strength, which could take six months or more.”

Meanwhile, Donny’s older brother Merrill, 60, has replaced him on stage. Donny hopes to rejoin Marie at Caesars in Atlan­tic City from July 29 to Aug. 11, said the source.

“But if Donny’s doctors won’t OK him to go back to work, the Atlantic City show will have to be rescheduled,” said the source.

If Donny can’t rejoin the show, Merrill – who’s struggled on stage – may be replaced by another Osmond brother, either Jay, 58, or Jimmy, 50, added the source.

But Donny is said to be in no rush to get back to work with his famous sibling.

“Since Marie lost her talk show, she’s been taking her frustrations out on everyone around her, especially Don­ny,” said the source.

“He just couldn’t take it anymore and told a friend, ‘With the way Marie’s been acting, I’m certainly in no hurry to get back on stage with her.’

“But Marie’s desperate to hang on to the Flamingo show. She knows that audiences want to see the Donny and Marie magic – not just Marie, or Marie with a different Osmond brother.

“She’s terrified this could be the end of Donny and Marie!”