(CNN) As the end approached, Katie Prager spoke to her husband from afar, unable to be with him.

Dalton Prager, the husband from the real-life "Fault in Our Stars" couple, died Saturday afternoon at Barnes-Jewish Hospital in St. Louis at the age of 25, his parents told CNN.

Katie was in hospice in Flemingsburg, Kentucky, when her husband passed away. The couple FaceTimed as Dalton was dying, said Debra Donovan, Katie's mother.

"She told him that she loved him," Donovan said. "We don't know if he heard her."

"Dalton fought a long hard battle with cystic fibrosis," Katie posted on Facebook . "He was a courageous fighter and 'give up' wasn't in his vocabulary."

Dalton had been in the intensive care unit on a ventilator for about two weeks before he died.

Just last week, the family had hoped to have a medical transport company fly Dalton from Missouri to a hospital in Kentucky. They wanted him to recover there, and then drive to their home, where Katie is receiving hospice care.

But in the end, Dalton was never healthy enough to fly to Kentucky. They were never able to reunite for a final kiss.

The last time Katie and Dalton saw each other was July 16, their fifth wedding anniversary.

A risky meeting

Katie and Dalton's romance began online when they were both 18.

The started to fall in love as they communicated on Facebook, but they knew meeting in person would be dangerous for Katie.

Dalton had Burkholderia cepacia, a highly contagious infection for people with cystic fibrosis. Katie didn't.

Her doctors warned her not to meet with other CF patients, for fear of contracting the bacteria. Still, Katie asked Dalton to visit her in Kentucky.

"I told Dalton I'd rather be happy -- like really, really happy -- for five years of my life and die sooner than be mediocre happy and live for 20 years," Katie said earlier. "That was definitely something I had to think about, but when you have those feelings, you just know."

Two years later, in 2011, Dalton and Katie married. Both were 20 years old.

Katie did contract Burkholderia cepacia, and the husband and wife waited for transplants at the University of Pittsburgh Medical Center. Dalton's came first, on November 17, 2014, and it was a success. In July 2015, after a long fight with Medicare, Medicaid and her hospital, Katie got her transplant, too.

But their medical struggles continued. Dalton seemed to do well at first after his transplant, but then developed lymphoma. He overcame the cancer, but then was recently hospitalized with pneumonia and a viral infection.

Katie's transplant never worked well. She was in and out of the hospital, and earlier this month doctors told her there was nothing more they could do.

Five years together

Now there are the memories of Dalton, a friend to everyone, who loved to cook, travel and go antiquing. He dressed sharply, and enjoyed spending time outside in nature.

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Photos: A real 'Fault in Our Stars' couple Photos: A real 'Fault in Our Stars' couple Katie and Dalton Prager met when they were 18; both had cystic fibrosis. Hide Caption 1 of 8 Photos: A real 'Fault in Our Stars' couple The two wanted to meet even though people with cystic fibrosis can easily share dangerous lung infections. Hide Caption 2 of 8 Photos: A real 'Fault in Our Stars' couple The Pragers were married two years later. Hide Caption 3 of 8 Photos: A real 'Fault in Our Stars' couple One month after meeting, Dalton had passed a dangerous infection on to Katie. Hide Caption 4 of 8 Photos: A real 'Fault in Our Stars' couple A year after their wedding, the couple were too sick to work and had to quit their jobs. Hide Caption 5 of 8 Photos: A real 'Fault in Our Stars' couple They both needed new lungs. Hide Caption 6 of 8 Photos: A real 'Fault in Our Stars' couple Dalton had his transplant first. Despite his infection, the transplant in November was a success. Recently, he was hospitalized in St. Louis with pneumonia and a viral infection. He died September 17, 2016, at age 25. Hide Caption 7 of 8 Photos: A real 'Fault in Our Stars' couple After months apart from Dalton, Katie found out she would receive a lifesaving lung transplant. She was able to briefly reunite with her husband afterward. She died at her home in Kentucky on September 22. She was 26. Hide Caption 8 of 8

Katie fell for his smarts, his good looks and his charming personality. Days after they started talking online, she knew she would marry him. Nobody had ever made her feel that way before, she said -- like she was the only girl in the world.

"He was one of the greatest people I'd ever met and not many people like Dalton come around so you got to get him while you can," said Katie, now 26.

The day before Dalton died, Katie told CNN she had no regrets about their decision to meet in person. For all the time spent sick or in the hospital, it's the time they spent together that stands out to her.

"It gave me some of the best years of my life," she said. "I'd rather have five years of being in love and just really completely happy than 20 years of not having anybody."