A FOUR-year-old boy has thanked supporters for their help getting him pioneering cancer treatment in the United States after becoming free of the disease.

Zac Oliver told his thousands of followers in a video posted on Facebook: "Guess what everyone, I have no cancer."

He was diagnosed with a rare form of leukaemia in May 2018 and he was taken to a hospital in Philadelphia in November.

Doctors there gave him a 60 to 80 per cent chance of survival.

Zacís family said he wasnít able to be treated on the NHS because he didnít meet strict requirements.

After The Sun revealed the family needed £500,000 to pay for treatment, donations began flooding in.

The campaign received a £50,000 boost from Simon Cowell and got over the line when a mystery donor came forward with £100,000.

Zacís mum, Hannah Oliver-Willetts, said the donor told her: ďIt doesnít matter who I am, start arranging flights because Iím going to make it up to £500k. This is not a prank.Ē

The cash was deposited in hours and the youngster was able to begin treatment for acute lymphoblastic leukaemia.

Dad Mark Garbett told the BBC doctors have genetically modified his immune system and "trained it to go and hunt and fight cancer".

Zac came back to the UK while the hospital engineered the cells and then returned for the next stage.

Mark said has been confident the treatment would be successful but added: "We were trying not to think of what would happen if it didn't work."

The family were this week told the hospital the treatment had worked and they came home yesterday.

"Everything that they said that they expected to happen - and all the processes they expected us to go through - happened," said Mr Garbett.

He said thankfully there very minimal side effects from the treatment.

"He's up and about, running around - he's the Zac we used to know, so full of energy again. He's cancer free, and we are praying it will stay that way."