Morgan Carey has branded his famous sibling selfish for refusing to help Alison Carey, a former prostitute who is HIV positive and in need of brain and spine surgery.

"Your sister is dying and she is struggling and where are you?" he tells Britain's The Sun newspaper. "You think you are so fabulous, but you are a witch.

"Mariah needs to step up. I flew in from Hawaii last year when Alison was taken off a ventilator, believing she was going to die. My sister didn't even show up at the hospital. Thankfully Alison had a miraculous recovery but now she needs brain and spinal surgery and will be going into hospital any day."

Alison has had little contact with her famous sibling since they fell out in 1994. She revealed last year (15) she last spoke to the Hero hitmaker in 2010, when the singer arranged to treat Alison's son and daughter to a dessert date in New York City, but they have not been in touch since. Alison subsequently penned an open letter to Mariah, but she has yet to respond.

"Alison has desperately reached out to Mariah over and over again," Morgan claims. "We never hear back."

Morgan explains he had a falling out with the Hero star after he tried to warn her against marrying her ex-husband Nick Cannon, because he believed the entertainer and TV presenter was only after her money.

She is now engaged to billionaire businessman James Packer, and Morgan, who heard the news via social media, questions whether she is truly in love with the Australian.

"I have not spoken to Mariah in two and a half years," he adds. "I only heard she was getting married through social media. I don't even think Mariah is in love with James, she's only in love with herself. She is evil. She has always been that way. It's her £5 million engagement ring she is in love with. It is so tragic that while she is out flashing her big diamond ring to anyone who will pay attention, she can't lift a finger to help her dying sister."

"The money I'm talking about is just small change to these people," he continues. "Why isn't our millionaire sister and her billionaire fiance helping out? I think she could at least manage to put our sister in a good hospital and make sure she gets the care she needs."

But despite their estrangement, Morgan still wishes Mariah well.

"When I think of Mariah, in spite of all her shortcomings and her betrayals of me, I think of her with pity and compassion, because I know how she had to grow up," he concludes. "I have no idea if her marriage is going to be any more successful than her first two, but I wish her the best and a good life. I'm just happy to live in Italy away from it all."

A representative for Mariah, who was also married to music mogul Tommy Mottola in the 1990s, has reportedly refused to comment on Morgan's allegations.