Queen Elizabeth II's official cause of death might never be revealed, as Buckingham Palace remains tight-lipped on the circumstances that precipitated her passing.

But medical experts told News Corp frailty and "geriatric syndrome" may have contributed to her declining health.

Officially though, the royal family announced that the 96-year-old had "died peacefully" at Balmoral Castle in Scotland. More specific details have not been provided.

In the hours prior to her death, a statement from Buckingham Palace said that her doctors were "concerned" for her health and "recommended she remain under medical supervision".

Adding that "the Queen remains comfortable and at Balmoral."

However, according to medical experts, the Queen would have likely been a "typical case" on the UK NHS' Frailty Index.

The scale is used to track and monitor symptoms like increased immobility, falls and weight loss in "people aged 65 and over who may be living with varying degrees of frailty".

The NHS states that frailty describes "how our bodies gradually lose their in-built reserves, leaving us vulnerable to dramatic, sudden changes in health triggered by seemingly small events such as a minor infection or a change in medication or environment".

A purple bruise noted on the Queen's hand could have been a sign of peripheral vascular disease. Photo / Getty Images

• Mark Sainsbury and Fleir Fitzsimons on Queen Elizabeth II edition of Friday Faceoff
• Touching moment the Queen broke royal protocol

Under the Prisma-7 test, the Queen had met five out of the seven criteria which would have classified her as frail. This included that she was over 85, had ongoing health problems, required regular help, had been forced to cancel activities and used a walking stick.

Medical experts also told News Corp that the Queen could have also presented as a case of "geriatric syndrome", in which a mixture of symptoms, "rather than one specific illness", was the cause of death.

Speaking on Weekend Sunrise on Sunday, GP Ginni Mansberg said the Queen could have also died from a stroke or heart attack. Behind dementia, the two conditions are the second and third biggest killers of women, Mansberg said.

The GP said it was understandable that the Queen would have had to reduce her royal duties over the past year.

"She was losing some weight, she was walking with a stick.

"As you get older you are frailer, you don't have as much muscle strength, you don't have as much energy … Doing the sorts of duties she had to perform would be taxing."

During one of her last official functions in the two days before her death, it was noted that the Queen had a purple bruise on her right hand while meeting the UK's new Prime Minister Liz Truss.

Speaking to the Daily Mail, Dr Deb Cohen-Jones said this could have been a sign of peripheral vascular disease.

"It's a blood circulation disorder that causes the blood vessels outside of your heart and brain to narrow, block, or spasm.

"It can sometimes result in heart failure. If your peripheral circulation is that poor, organs aren't receiving a good blood supply. It can be a sign of multi-organ failure."

If she had this, it's unknown how long the Queen might have suffered from the potentially painful condition, as the monarch frequently wore gloves when outside.

In June, the monarch also missed the official church service at her Platinum Jubilee celebrations due to complaints of discomfort. The Queen also contracted Covid in February.