The parents of little Oscar Knox have said they are heartbroken after being told his cancer has returned.
Stephen and Leona Knox were given the devastating news during a trip to Scotland.
It comes less than four months after they were told their son was disease-free.
Leona said they were "shocked, scared and overwhelmed" by the news.
"It's not good, we are totally heartbroken and very frightened about what lies ahead," she said.
Four-year-old Oscar has touched the hearts of thousands with his brave fight since being diagnosed with high-risk neuroblastoma – a rare and aggressive childhood cancer – in November 2011.
His parents went public in a bid to raise awareness and funds for Oscar's care.
A huge support campaign was launched, backed by celebrities including Olympic medal-winning boxers Paddy Barnes and Michael Conlan.
In April Stephen and Leona revealed he had been given the all-clear.
However, on Thursday night Leona said the illness was back.
Writing on the Oscar Knox appeal website, she said: "We've had some terrible news – Oscar's cancer has returned, the disease is extensive, and it's spreading rapidly.
"We found out six days ago that he had relapsed after suddenly developing symptoms during our last few days in Scotland.
"We saw the full extent of it in the scans he had today. It's not good, we are totally heartbroken and very frightened about what lies ahead."
Leona said the news had come as a devastating blow, adding: "Stephen and I are shocked, scared, and overwhelmed by this news. We thank everyone for their incredible ongoing support, but need space and time to deal with everything."
She said Oscar now faces another tough battle.
"Our little man is in excruciating pain, not eating or drinking, and finding it very difficult to walk," she added. "The priority right now is to relieve his pain with regular and increasing morphine, and to decide on and begin a treatment plan ASAP.
"We have some very difficult choices to make, but more importantly, Oscar has another incredibly tough battle on his hands.
"Please, please send every positive thought you have our way, and support our brave wee Oscar as he fights for his life once more."