World's oldest conjoined twins Lori and George Schappell dead at 62: Sister and her transgender brother whose skulls were fused together pass away in Pennsylvania - after defying doctors who said they wouldn't live past 30

The world's oldest conjoined twins Lori and George Schappell have died at the age of 62.

Lori and her transgender twin George passed away on Sunday at a hospital in Pennsylvania due to undisclosed causes, per their online obituaries.

The siblings, who had partially-fused skulls and shared 30 per cent of their brains, defied doctors who said they wouldn't live past the age of 30.

The twins had previously made headlines after George, formerly Dori, came out as transgender.

Lori was able-bodied but George, who had spina bifida, was confined to a wheelchair which his twin pushed around.

He had enjoyed a successful career as a country singer but Lori pursued her interests elsewhere as a trophy-winning ten-pin bowler.

She also worked at a hospital laundry for several years during the '90s, arranging her schedule around George's gigs, which took them around the world to countries including Germany and Japan, according to the Guinness World Records.

The siblings became the first same-sex conjoined twins to identify as different genders after George, whose original name was Dori, came out as a transgender man in 2007.

It was at this point that he changed his name from Reba - a moniker he took up to honor his idol Reba McEntire because he disliked their rhyming names - to George. 

The twins lived independently in a two-bedroom apartment in Pennsylvania where they took turns practicing their separate hobbies.

They alternated whose room they slept in and also showered separately by using the shower curtain as a barrier as one stood outside the bath.

The pair appeared on numerous shows including Jerry Springer, The Maury Povich Show and The Howard Stern Radio Show. 

In the past, when asked if the death of one would necessarily mean the death of the other, Lori said at the time: 'No, it would not. That's another misconception.'

George, then Reba, explained in the 1997 documentary: 'If it's caught early enough, we could both be rushed to the hospital and then in an emergency, quickly be separated to save the other one.'

Elaborating further on whether they had ever wished to be separated, he said no: 'Would we be separated? Absolutely not. My theory is: why fix what is not broken?' 

'Just because we cannot get up and walk away from each other doesn't mean that we cannot have solitude from other people or ourselves,' Lori added. 'People who are conjoined can have a very private life.' 

She also shared her dreams of one day having a family of her own, explaining: 'Eventually I would love to have myself a family - a husband and children of mine.'

Interviewer Antony Thomas then asked George whether he would share the intimacy with any future husband, to which he replied: 'He would be like a brother-in-law to me, that's it. They can do whatever they do and I'd act like I'm not even there. I would block it out.'

The twins defied all the predictions of medical professionals who said that they wouldn't live past the age of 30.

They became the oldest female conjoined twins ever in 2015, overtaking Masha and Dasha Krivoshlyapova who died aged 53.

Lori and George are survived by their father, six siblings, several nieces and nephews.

It comes after conjoined twins Carmen and Lupita Andrade, 23, based in Connecticut, detailed what happens if one of them dies.

The sisters, who moved to the US from Mexico when they were two, share all organs and limbs below the waist.

When they were born, doctors told their parents that they would likely only live a few days - but they have defied all odds and are now thriving.

Carmen recently discussed some of the confronting and gritty messages they regularly receive - including what will happen if one of them dies. 

'We share a bloodstream, so eventually sepsis will kick in and obviously within hours or days the other one will die,' she explained. 'But we’re not dead, so why always ask us that?'