"We are delighted to share that the Car-T cell therapy has been successful and we are now home with all his medical attachments out."
But 21 months later, William succumbed to his cancer and died last week.
While the fight to save William had come to an end, they had since been embroiled in a new fight - to get William's aunty, Nicole Seymour, to Auckland to attend his funeral.
She has had her travel exemption application declined twice by the Ministry of Health as the online form only allowed for immediate family to get through.
William's father, Marcus, told Mike Hosking that it had been "ridiculous" dealing with the Ministry of Health's online forms getting exemptions for family to attend his funeral.
Marcus said they had been denied twice and there was nowhere on the ministry's online form where people could click for extended family.
As for what he will do today, Marcus said "cry".
Everyone was vaccinated and had negative Covid tests.
They'd all been following the rules and William had been sick for six years so they were keen to make sure they were doing things right.
He was gutted that the form wasn't set up for a child dying or a child being sick, he said.
National's Whangaparāoa MP Mark Mitchell told Hosking it was "a tragic, horrible case that highlights how broken the MIQ system is".
Mitchell said it was unfortunate as the ministry appeared to have not given the people involved in the service the appropriate training to help make decisions.
"I've had several cases like this and we have lost the human side, for whatever reason, in terms of how we're dealing with these cases. The cases that I've dealt with, the risks are so low, they're minimal, and yet they seem to be just employing a blanket approach to it and forgetting about the human side to it, the emotional toll.
"As we emerge out of this, there's a massive human toll that could have been avoided if we had a much more sensitive approach to how we're dealing with these cases."
Regional Development and Tourism Minister Stuart Nash said he didn't know about the case so couldn't comment.
"It's a real tragedy and my heart goes out to the family," he said on Newstalk ZB. "I can't comment on this because I don't know the processes the father's gone through."