Kate Hudson has gained the title of "best friend" after taking to Instagram to promote her friend Sara Foster's swimsuit collection.
MORE: Goldie Hawn and Kate Hudson are twins in rare family photo inside stylish home
The mother-of-three put on a two-piece from her friend's company, Summersalt, and proudly showed it off to her followers. Posting two photos of herself wearing 'The Sara Foster String Bikini Top' and 'The Cheeky High Leg Bottom,' she wrote: "My girl @sarafoster giving us some spring time cotton candy in a swim suit collection! Love it, Love you."
WATCH: Kate Hudson reveals private sauna at $5.5million home
Fans rushed to comment on the snaps, with many in awe of her body and wanting to know her fitness and diet secrets.
MORE: Kate Hudson delights fans with rare photo of Kurt Russell during family day out
READ: Kate Hudson's baby number 4 - everything she's said
"What is your diet? I need to do it," wrote one, whilst a second added: "How are you so taut after 3 children. Amazing."
A third remarked: "Wow! You look fantastic! You don't look like you had any children."
The Sara Foster String Bikini Top, $65, Summersalt
Kate has been very honest in the past about the secret to her trim body. In a recent interview with Women's Health she revealed that WW (formerly Weight Watchers), for which she serves as an ambassador, has allowed her to transform not only her body but also her relationship with food.
"I make beautiful meals that have no points, then I can indulge," she explained. "I'll do a whole day eating amazing Zero Point foods [like chicken and leafy greens], then I have wine and ice cream."
The star was supporting her friend Sara Foster's company, Summersalt
The Hollywood star has also become a proponent of intermittent fasting, not for weight loss she tells the magazine, but for energy.
As for exercise, Kate often chooses Pilates or one of Tracy Anderson’s classes. The star has found that Tracy's workouts have helped "my skin attach back to my muscle".