The 'Chandelier' hitmaker adopted two 18-year-old boys last year, just before they aged out of the foster care system, and she has revealed her family has grown by two once again.
"My youngest son just had two babies. I'm a f**king grandma!" Sia exclaimed during a chat with Apple Music's Zane Lowe.
"I'm trying to get them to call me 'Lovey,'" she added, explaining she stole the idea from pal Kris Jenner, who has 10 grandchildren.
The new arrivals aren't the only reason Sia has been celebrating: "One [son] recently came out, and he's just blossoming and is the light of my life... I love him so much."
While the musician has been enjoying bonding with her "fantastic" boys, who are both Black, their relationship was a little rocky at first as she tried to learn about their lifelong struggles, bouncing from one foster home to another.
"They've been in 18 different locations in their 18 years," Sia said, insisting the foster care system is "completely corrupt" and "failing" those who rely on the service.
As a result of the trauma they've suffered over the years, the Australian star has been forced to have multiple emotional conversations with her sons to try and keep them out of trouble with the authorities.
"I'd say, 'I'm doing this because I'm your mother. I love you. I don't want to see you in prison... With your history and the colour of your skin, I don't want to see you as that five per cent that ends up in prison for life. I don't want that for you,'" she recalled.
Raising two Black teens has also made Sia more aware than ever about the importance of the fight against racial injustice, and her new role has inspired her to step up her activism for the Black Lives Matter movement.
"I'm embarrassed that it took me to adopt two Black sons to really understand what they go through on a daily basis," the artist confessed through tears, admitting she is "very scared" for her boys.