Kate Hudson's young son shaved her head for Sia project

Kate Hudson's son Bingham Bellamy shaved her head for her part in an upcoming Sia project.

The actress is starring in the Australian musician's debut feature film Sister, reportedly based on a one-page story she wrote about a drug dealer and his autistic sister.

Kate was required to lop off her signature blonde tresses for her role in the movie, and revealed during an appearance on Jimmy Kimmel Live! on Thursday (12Oct17) that she left the task up to Sia and her six-year-old son, whom she shares with ex-fiance Matt Bellamy.

"I love it. It was funny too, because when I first started I didn't think about it because it was for the role," she smiled. "It was like, 'Let's do this.' And then as we were shaving it, and Bing - my little one - and Sia were doing the honors of shaving the head. They couldn't really go wrong."

Kate explained that she wasn't anxious about undergoing a bold new look until it occurred to her that her head maybe a funny shape. Thankfully,

"I didn't think about it until it started, and (then I pondered) what is the shape of my head going to look like? And I really started to panic. And Sia was like, 'I know it's going to be round, I know it,'" she shared. "And all of a sudden it was like a birthing, it was like, 'It's round!'"

In addition to discussing her latest Hollywood projects, Kate also talked about her new book, Pretty Fun: Creating and Celebrating a Lifetime of Traditions, which offers up tips and inspiration for celebrating special moments. The star also recalled some of the best parties she's been to over the years, including a time when she was a teenager and her actress mother Goldie Hawn turned up unexpectedly when she was throwing a bash with her friends.

"We were having a blast. And all of a sudden, the door flings open and it's my mother. She was in a negligee, which was really weird. And she looked around as you would think she would in one of her films," she laughed. "And then she goes to the light and turns the lights way down and goes, 'Kids, lighting is everything.' And then she left and everybody was like, 'Your mom is so cool!'"