Jhoanna Buendia, an intensive-care unit nurse in England, said her aunt Araceli Buendia Ilagan, 63, had died of complications from the virus on Friday.
Buendia Ilagan had been a nurse manager in the surgical ICU at Miami Jackson Memorial Hospital in Florida for three decades, Buendia said.
Tune into ABC at 1 p.m. ET and ABC News Live at 4 p.m. ET every weekday for special coverage of the novel coronavirus with the full ABC News team, including the latest news, context and analysis.
Miami Jackson Memorial hospital called Buendia Ilagan a "hero."
Buendia said that Buendia Ilagan had called her just a few days earlier to check on her and also mentor her on how to care for patients with COVID-19 in the U.K.
"It's very shocking ... It's very terrifying. It's all mixed (emotions) ... I just can't find the right words to explain how I feel right now," Buendia told ABC News on Monday.
"She told me she's doing fine ... Never did I expect that that would happen to her," said Buendia, who also said her aunt had doted on her because she never had children.
Jhoanna Buendia told ABC News that she was afraid to return to work after her mentor/aunt died in Miami of COVID-19.
"To be honest, I'm terrified for my life," she said. "Especially (because of) what happened to my aunt. I mean, life is really unexpected. However, in my profession, we did a pledge that we have to stay strong, we have to take care of our patients no matter what and I'm sticking to that pledge ... It's our job."
Buendia said her aunt, the stalwart nurse, who never complained or showed frailty, had mentioned nothing about the illness or even that she had been feeling symptoms.
Her niece said she was shocked with the devastating speed with which the virus killed. By the time she arrived at the hospital, Buendia said, her aunt Buendia Ilagan was so sick that she died as soon as she got to Jackson Memorial.
"Her husband told us that he just saw her on the floor and she is not breathing properly anymore," Buendia told ABC News on Monday. "He just rushed her to the hospital. And then everything came so fast ... He's so shocked ... In her case, I'm very surprised because I didn't know that she's already feeling something."
Buendia told ABC News that although she was frightened to return to work, she would be returning Tuesday because her hospital was understaffed.
Buendia did say she felt safe at her place of work because her hospital followed strict protection protocol and had adequate PPE, personal protective equipment.
In New York, Dr. Russell Weg said that his 63-year-old father, gastroenterologist Dr. Arnold Weg, had likely contracted the virus, when a patient coughed on him. His father remains hospitalized.
"This was about four weeks ago. A longtime patient of his called with a worsening chronic cough. This was when there were just about a few hundred cases in New York City ... The patient called and as any doctor would, he had the patient come into the office ... During the exam the patient coughed on my father to no fault of his own, and we feel pretty confident that that was his exposure ... A few days later, about five days later, my father learned that the patient was admitted to the hospital. It was about a week after that exposure that my father started exhibiting signs of the coronavirus," Dr. Russell Weg said.
He said that his father developed a fever and leg cramps and that within a few days, he had to be rushed to the hospital and placed in the ICU.
Dr. Russell Weg told ABC News that Dr. Arnold Weg, a grandfather of six as well as a marathon runner, was "truly in the fight for his life."
"It is not easy to step into that ring when you know that the outcome can be fatal," Dr. Russell Weg said.
He said that his father, who had treated tens of thousands of patients and also trained health care workers, had spent a career running to the hospital in the middle of the night for emergencies.
"I know that my father, God willing he does get through this, he is going to jump back on the front lines and help as many patients as he can," Dr. Russell Weg said.
ABC News' Jessica Mendoza contributed to this report.
This report was featured in the Wednesday, April 1, 2020, episode of “Start Here,” ABC News’ daily news podcast.
"Start Here" offers a straightforward look at the day's top stories in 20 minutes. Listen for free every weekday on Apple Podcasts, Google Podcasts, Spotify, the ABC News app or wherever you get your podcasts.