Their love story is one for the books. Two 20-something individuals who met online, fell in love, and eventually got married. It sounds too common these days, but their story is extraordinary. 

Dalton Prager and Katie were both born with cystic fibrosis. It is a genetic disease that affects the lungs. It is a life-threatening disease that clogs the lungs with mucus and makes it difficult for the person to breathe. A person afflicted by this has an average life span of 40.

He was only 25 when he passed away last Saturday succumbing to his disease.

The couple became widely known as the real life version of the book turned movie "The Fault in Our Stars." They met in 2009 through Facebook and communicated online due to the health risks involved.

Dalton had an infection from having cystic fibrosis while Katie did not. They knew that if they meet in person, Katie might contract the same infection.

According to CNN, Katie said, "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, that was definitely something I had to think about, but when you have those feelings, you just know."

The two got married in 2011 and Katie got infected with Burkholderia Cepacia.

They were together for five years and both got lung transplants. However, Katie's transplant did not go too well and she was in and out of the hospital and was moved to hospice care after the doctors told her there was nothing they can do. Dalton's transplant was better but he got hospitalized and was on a ventilator for weeks before his death. People reported that the couple never fully recovered from their transplants.

They last saw each other for only a few minutes on their anniversary in July. Although Dalton had wanted to fulfill his wife's wish of a visit from him, he was never well enough to do so. He died without having to see his wife one last time.