Sia had only intended to adopt one child, but was convinced to adopt two when the boy she wanted to take home asked if his "cousin" could come too.

The 44-year-old singer opened up to InStyle magazine about adopting the teenage boys last year and shared a picture of herself with younger son Che, and admitted that she found her other son while watching a documentary about the foster care system.

"When I saw him, I said to myself, 'That's my son,'" she smiled. "I knew I wanted to help him. By the time I found him, he was 18 and ageing out of the foster care system. I told him that I wanted to adopt him, and since he was an adult, he left with me that day.

"The only thing he asked was if he could also bring his cousin Che, who had lived with him in a group home. I had two spare bedrooms, so I said, 'Sure!' And even though I’d never met Che before, he also moved in with me that evening.

"Later I found out that they weren’t really cousins, just friends. But I didn’t care at all. I just felt so blessed to have them both with me. And I’ve realised over the past year that Che was meant to be my son too."

Sia also recalled her first meal with her boys and Maddie Ziegler - the young dancer who the Chandelier star considers almost "like my daughter".

"Sitting at the table, my sons said, 'We're allowed to use knives here?' In foster care, they hadn't been allowed to use a metal knife to eat in years. And they'd never really eaten a vegetable either," she explained.

"I basically sat them down that day and said, 'What has happened to you in your life was wrong. It never should've happened. But my job now is to protect you, and we're going to get through everything together.' Both my boys had tears in their eyes, and from that moment on, I knew it was my duty to be the best mother I could be for them."