BELOVED former first lady NANCY REAGAN is facing a new medical nightmare that could hasten her death, say sources.

The brave 92-year-old is suffering from chronic obstructive pulmonary disease, which makes it difficult to breathe.

The debilitating disease recently forced her to cancel a charity lunch date with old pal Betsy Bloomingdale.

Sadly, the incurable ailment can be “incapacitat­ing,” says one expert.

“It is a slowly progressive lung disease,” explained Dr. Samuel Jacobson, a pulmonary specialist based in Boca Raton, Fla. “Patients often die from other conditions complicated by COPD.”

The condition can prevent patients from performing even basic activities, such as walking, cooking or even caring for themselves.

“This is a relatively new medical problem for Nancy,” said an insider. “But it’s deeply disturbing, given her age and how frail she’s become.”

Sources revealed to The ENQUIRER that Nancy’s COPD was one of the main reasons she was unable to attend the April funeral of the Reagans’ dear friend, former British Prime Minister Margaret Thatcher.

On May 9, Nancy appeared frail and shriveled when a nurse accompanied her to lunch with Larry King and his wife Shawn at a Beverly Hills restaurant.

And on June 5, a somber Nancy was photographed in a wheelchair as she commemorated the ninth anniversary of her husband Ronald Reagan’s death, placing roses at his grave site.

“After that, her health seemed to take a turn for the worse,” said the source.

She rarely gets out, but on July 16, she was spotted being assisted from a car to a wheelchair at The London West Hollywood hotel in L.A.

Nancy previously broke several ribs in a fall at her home in March 2012, and she suffered a fractured pelvis and sacrum in a 2008 tumble.

Her deteriorating condition isn’t being helped by family members who are said to already be fighting over her $15 million estate, as The ENQUIRER reported.

“The kids should be spending more time with their mom and less time bickering,” noted the source. “They may not have much longer with her.”