(CNN) - — For most couples, a wedding day is one of the most joyous days of their lives. But for one Pennsylvania couple, this day is bittersweet.
You see, the couple's best man is dying. And he's only 2 years old.
Christine Swidorsky and Sean Stevenson had delayed their wedding because their son, Logan, was sick.
Logan has leukemia and doctors recently told the family Logan has just a few weeks to live.
So his parents decided to go ahead with their wedding, and Logan was their best man at Saturday's event in Jeannette, Pennsylvania.
"We waited for this day for a long time ... but under the circumstances with Logan being sick all the time, we just held off. We just knew he was gonna get better," the groom told CNN Pittsburgh affiliate KDKA. "But under the circumstances of what the doctors told us, we just decided to go ahead and do it while he is still with us."
Friends of Swidorsky and Stevenson took over, donations poured in thanks to a Facebook post, and the wedding became reality within a week.
Logan, dressed in a tan suit with an orange shirt that matched his mom's bouquet, looked on as his parents exchanged vows and rings in the family's back yard.
Though he wasn't feeling well, Logan's mom, Christine, said "This is our dream come true, all our family together celebrating. This is a celebration of Logan's life and a celebration of our marriage."
Christine often talks about how Logan's a fighter who's always stayed strong. Before the wedding, she told CNN her son's story.
Born on October 22, 2010, he weighed just three pounds. Eating troubles kept Logan in the hospital, but he kept fighting, kept growing, and was soon home with his parents and his two older sisters.
Christine originally hoped to call him Sean, after his dad, but Sean disagreed. So one day, while leafing through a baby naming book, Sean stumbled onto "Logan," and it felt perfect to them both.
And for his first year, he grew, he was healthy, and he made his family unspeakably happy. Even today, as his life nears an end, Christine struggles to find words to say what an amazing little boy he is.
Just after Logan's first birthday, Christine noticed that he wasn't feeling well again, and his lips and fingernails had turned white. Over the course of a month, she took Logan to the pediatrician four times before the head pediatrician tended to him. When he did, he quickly called 911.
Christine says Logan shocked doctors at Children's Hospital of Pittsburgh. His leukemia had progressed so far, they were surprised he was still alive. Chemotherapy was started right away, taking an extraordinary toll on his body.
Sean and Christine learned more devastating news shortly after: Logan has a genetic disorder called Fanconi anemia, which most frequently results in death, most commonly from cancer, between the ages of 25 and 30.
But Logan fought hard, just like he had done as a newborn. He landed in the ICU but pulled through, and by July 13, 2012, doctors were prepared to give him a blood stem cell transplant.
After his stem cell treatment, he was free of leukemia for nine months, eating and acting like any other child. Life started to feel normal for Logan's family, but Christine's gut feeling returned when she saw Logan acting strange again.
It was cancer again: a mass the size of an orange on Logan's larger and better-functioning kidney. Doctors had no choice but to remove the kidney, just a week before Easter of this year.
Life gained a long-sought-after normalcy for Logan and the family, except for the twice-weekly visits to a clinic for his chemotherapy. The therapy, though not a perfect solution for Logan, would hopefully prevent a recurrence of the cancer, despite being a lower dose than average.
Logan's life continued to improve. "He was eating bowl after bowl" of spaghetti, "it was a wonderful feeling," Christine said.
But then he started getting fevers, then throwing up. His left side swelled as the mass returned, where the kidney once was. "I thought he was doing so well ... it's like you take two steps forward, 15 back," Christine said. The doctors told Logan's family that they could only do more harm than good.
And in June, as the family's fortunes continued to fail, the Make a Wish Foundation gave them a trip to Disney World. But after just four hours there, Logan was back in the hospital. Eight days of torture ensued, as he had developed an infection and eventually needed to be flown home to Jeannette, about 40 minutes from Pittsburgh.
Finally, on July 26, doctors gave Logan one to two weeks to live.