Viewers were moved last month by a heartwarming video of 8-year-old Tomas MacCurtain helping his sister Abby slam dunk a basketball.
Over 8 million watched after dad Greg MacCurtain of Plymouth, Massachusetts, posted the sweet footage of his kids onto Facebook.
"Tomas had the great idea to bring the rim to her," MacCurtain told "Good Morning America." "I had to record it. It was unbelievable."
This wasn't Abby MacCurtain's first encounter with sports. The 9-year-old competes in 5Ks with her mom Heidi, participates in triathlons with her father, and will even run the virtual Boston Marathon this fall.
At 10 months old, Abby was diagnosed with a terminal neurological disorder called Leigh's Disease.
Because of this Abby uses a wheelchair, though it doesn't stop her from being active with her brother and partnering up with dad in races.
"She loves it and it's a great way to introduce her to a sport," MacCurtain said, adding that Abby did her first triathlon at 5 years old.
In the first leg of races, the swim, MacCurtain swims while Abby sits in a one-person, inflatable kayak as her dad's firefighter colleagues act as her safety spotters.
In the second part, the bicycle race, Abby is harnessed into a 7-foot long bike.
In the last leg, Abby uses a Hoyt running chair. The device makes it easier for her to be included in athletic activities.
MORE: Mom attempts world record for fastest 10K with a double strollerWhen she's not racing, Abby enjoys being with her family.
"She's extremely happy all the time with people," MacCurtain said. "She's happy with her parents. She loves her brother and she loves school.
"One day all we're going have left is memories, unfortunately," he added. "When she was first diagnosed they gave two years for her to live and she just turned 9 over the winter. She's pretty much exceeding all expectations."
MacCurtain shares Abby's journey through photos and videos of her and Tomas' special bond on social media.
"They're amazing kids," MacCurtain said. "There's things that are not teachable and that's definitely [with] Tomas. How do you teach such kindness? He's got a great heart. They both do."