McCartney has added the neon pink Gemma Relaxing line to her lingerie range and Moss models it in a newly unveiled ad to raise awareness - and funds - for the fight against breast cancer.
Says the designer: 'I wanted to remind women that when they wear this set, the first thing they put on in the morning, to keep on top of their health and visit their doctor regularly. I wanted it to be the initial starting point of awareness of this terrible illness. Not only does the set serve as a healthy reminder, but it looks great, fits incredible well, and is comfortable and stylish.'
Kate was a natural choice to promote it - though not for the reason you might think.
'Kate is a strong feminine woman with a daughter and a husband; a strong family unit,' McCartney explains. 'For her it was important to bring awareness to this campaign to keep families together.
'Women are an integral part of the family unit, they keep and hold families together and are a source of strength.'
A percentage of the profits raised from the line will go towards funding a new Mammography suite at the Linda McCartney Centre in Liverpool - established for McCartney's mother, who died from breast cancer in 1998 - which provides innovative treatment, support and care.
Prices range for Gemma Relaxing range from £27 to £50, and it's available to buy now at stellamccartney.com, Stella McCartney stores and select department and specialty stores worldwide.