Alison Carey, a former prostitute who is HIV positive and in need of brain and spine surgery, is on her deathbed, according to brother Morgan, and he feels the time is right for the Hero singer to step up and give her sibling a chance of survival.

After calling Mariah "a witch" in a recent interview with Britain's The Sun newspaper, Morgan has now appeared on Dutch TV show RTL Boulevard, insisting it's high time the singer stopped "trying to be fabulous" and considered the plight of her sister.

"Mariah is someone who holds grudges and is not empathetic, is not compassionate, and sees the world through the filter of her own ego," Morgan told the TV show via Skype.

"It's heartbreaking for Alison... She has had a number of operations on her brain... She has had several strokes, she has seizures... She loses consciousness."

Morgan used his latest TV attack on his superstar sibling to request Mariah help fund her sister's fight for life, stating, "We're doing what we can because no other member of her family is stepping up to the plate."

And in a passionate, direct plea to the diva, her brother states, "Your own sister is struggling. She's on her deathbed with tubes down her throat.

"They're (doctors) giving her minutes, hours, days to live and you're partying it up with Elton John, trying to be all fabulous, splashing the $7 million (engagement) ring (she received after accepting fiance James Packer's proposal). I mean, come on, spend some time with your sister. Lean into what's right!"

Mariah has had little contact with Alison since the sisters fell out in 1994. Alison 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 told The Sun last month (Mar16). "We never hear back."

Morgan is also estranged from Mariah - the siblings fell out after he tried to warn her against marrying Nick Cannon.