To be told your four-year-old child is seriously ill must be every parent's worst nightmare.
But to be hearing the news for a second time – months after believing they would be fine – is beyond comprehension.
That is the heartbreaking ordeal which Leona and Stephen Knox have endured since learning in October 2011 that their son Oscar was suffering from neuroblastoma, an aggressive form of cancer.
Through the internet, they have been able to reach out to thousands of people, while providing a rare insight into the heartbreaking journey of a family dealt the cruellest of setbacks.
Leona, from Aghyaran in Co Tyrone, was studying business and information technology at Queen's University when she met Stephen, from Glengormley, who was doing a mechanical engineering degree. They were introduced by mutual friends on St Patrick's night in 2001.
They married five years later in December 2006 and settled in east Belfast. When Oscar was born two years later on September 10, 2008, the young couple's life seemed complete.
But their dreams were soon shattered.
As the weeks passed Leona and Stephen became concerned about his development.
He was later diagnosed with Jacobsen Syndrome, an extremely rare chromosome disorder said to affect just one in every 100,000 people.
Oscar made astonishing progress and eventually was on par with other children his age. He started playgroup in September 2011 – two days after his third birthday.
But then came news which every parent dreads.
After various spells in hospital, Oscar was diagnosed with high-risk neuroblastoma, a rare children's cancer which affects only one in every 100,000 children.
The family raised £250,000 to bring Oscar to America for cutting-edge treatment, but their hopes were dashed when he was diagnosed with a potentially fatal heart problem.
Leona and Stephen were twice told to prepare for his death.
But Oscar beat the odds to pull through and then, in a remarkable twist, appeared to have beaten the cancer which threatened to cut his life short.
But just a week ago, during a trip to Scotland, the family's joy was cruelly crushed.
Despite the agonising setback, Leona still found time to thank all those who have supported her son's battle for life over the last two years.
And there is also a hint of defiance, as the family prepares for another journey of uncertainty.
"Thanks guys, let's get TeamOscar back on the rollercoaster, and tackle this beast as the main man has previously shown us how. We love you so much Oscar x," she wrote.