Savannah Miller has become an ambassador for The Haven.
The 34-year-old fashion designer will support the breast cancer charity's Mother's Day campaign and Chelsea Flower Show garden, while also appearing at several other events throughout 2015.
Revealing the news on Twitter, she wrote: "Pleased to share that I am a @breastcancerh Ambassador.Cannot wait to show you what this wonderful charity does! (sic)"
Echoing the announcement, the charity - based in south Wales - said they are "delighted" the star has decided to lend a helping hand to their work.
They posted on Facebook: "We are delighted to announce that Savannah Miller has become a Haven Ambassador. A huge thank you to Savannah for her support."
The mother-of-three has worked with Alexander McQueen, Shanghai Tang, Betty Jackson and Matthew Williamson during her career, and launched her global brand Twenty8Twelve along with her sister, Hollywood actress Sienna Miller, in 2007.
As well as her fundraising work, the stylish star launched her label 'SAVANNAH' in 2012 and is now "working on a new line with a major high street retailer that will be launched for AW15 in September" according to the charity's website.
Savannah joins other celebrity supporters including actor Hugh Dennis, Gaby Roslin, Kimberley Walsh and Liz Green.