Singer Sia joked she was “horrified” at becoming a grandmother aged 44 after adopting two teenage sons last year.

The Australian musician, known for hits including Cheap Thrills and Chandelier, revealed she had adopted two 18-year-olds who were becoming too old for the foster system.

The younger of the men has welcomed two children. Sia announced the news during an appearance on Zane Lowe’s Apple Music podcast.

Sia has revealed she has become a grandmother (Joe Giddens/PA)

She said: “My youngest son just had two babies. I’m a f***ing grandma! I’m just immediately horrified.”

Sia, who often hides her face to remain anonymous, added: “They call me Nana. I’m trying to get them to call me ‘Lovey’, like Kris (Jenner). I’m like, ‘Call me Lovey’.”

Sia revealed in May she had adopted two sons who were “ageing out of the foster care system”.

Speaking to Lowe, the singer said she had been left “jaded” by her experiences with the system.

“It’s completely corrupt,” she said.

“It’s failing us. Not in my experience, in my sons’ experience. They’ve been in 18 different locations in their 18 years.”

Sia said her sons, who are black, have “bloomed” since leaving foster care and discussed  the impact the Black Lives Matter movement had had on her.

She said: “I’m embarrassed that it took me to adopt two black sons to really understand what they go through on a daily basis.”