Billy Green, from Wakefield, was first diagnosed with Acute Myeloid Leukaemia when he was three years old.
After having chemotherapy, radiotherapy and a bone marrow transplant on his fifth birthday, donated by his then three-year-old sister Willow, he was given the all clear.
But he began to suffer with knee pain in January 2019 and in November the family received the devastating diagnosis that the leukaemia had returned.
Now 11, Billy was living an active life and loved singing, performing and going to youth club.
His mum, Lisa Green, said: "It had been six years since the all-clear and it's really knocked us. We'd just started to not worry as much and started loving life, actually doing things.
"Now we're just back to square one."
Billy was in hospital over Christmas having chemotherapy and will undergo twelve rounds of radiotherapy, before doctors hope he can have another bone marrow transplant.
But he suffered a set-back after catching a serious infection last week, which caused fluid on his lungs.
Lisa said: "He had loads of mucus in his chest and throat and told me and the nurse he was really scared.
"He turned and asked me that dreaded question - 'am I going to die?'
"He's such a good kid and we're just heartbroken that he's older and having to go through this again."
Billy is now on morphine and doctors have seen an improvement to his health, and the family hope a message or a visit from his hero Lewis Capaldi will make his 'dreams come true'.
The 11-year-old loves singing along to the Scottish singer's hits and Lisa has been amazed by the support on Facebook, where she posts updates on Billy's journey.
Dozens of people have sent emails, messages and letters to Capaldi, urging him to reach out to Billy.
Lisa added: "It would just be amazing for Billy, he loves his music and he's always singing it.
"He has a wicked sense of humour and he's very grown up for his age - everybody fights over him at the hospital!
"It's been amazing to get the support from everyone, all the love and messages have been really nice."
A JustGiving page has been set up in support of Billy's family and can be found here.