Leukaemia

It's the first time the singer has spoken publicly about Johannah Deakin since she passed away from leukaemia in December.

"It was my mum who said to me that I've just got to keep going," he says in the interview with US station SiriusXM.

The former One Direction star was promoting his new single with DJ Steve Aoki.

Declan is in remission from leukaemia and recently spent the day with Australia's Federal Police.

He was collected from home in a motorcade, taken to the specialist response group headquarters where he took part in a hostage scenario.

Declan's parents say the experience gave the family something other than his treatment to focus on.

"He has been telling all our friends and family that he is going to blow stuff up and I think they've been really jealous of that," says his mum Belinda.

"He wanted to just blow something up and he did that, which was awesome."

It was in fact her grandson who put her on this path in the very beginning.

Mary had approached the Cecilia Ali Leukemia Foundation to climb Mt Wilhelm with 11 other women, to raise funds and awareness of the foundation and Leukaemia in PNG.

She was particularly passionate about this because she had lost her 12-year-old grandson Jedrick Moale to Leukaemia in April 30, 2014.

RNZ reports his Super Rugby club, the ACT Brumbies, announced today that Lealiifano is currently being treated in hospital.

The 28-year-old was a notable absentee from the Wallabies squad for the Rugby Championship named yesterday.

The Australian Rugby Union said it would do whatever it could to support him.

"We were shocked to receive the news of Christian's diagnosis yesterday and our thoughts are firmly with him as he begins his treatment," said chief executive, Bill Pulver.