Stella McCartney: 'I wanted to identify a new generation of young women who are more than just beautiful models; women who have something important to say. Grimes doesn't try to be anyone but herself so she was an obvious choice for the Pop campaign. We met in New York and our conversation wasn't what I would call light. We have a lot in common in that we care about sustainability, environmental responsibility and protecting the creatures around us through vegetarianism. She's totally uncompromising and reminds me a lot of my mother [the late musician and animal rights activist Linda McCartney] in that sense.

'Watching Grimes in front of the camera is so refreshing; she's very animated and in the moment. She came to the shoot for the Pop campaign with the top of her head purple and the bottom pink and said, "I dyed it last night, it didn't really come out right." We had the best hairdressers on hand and could have made her the perfect blonde but it's not who she is. It's not often women are allowed to be themselves in a beauty campaign. We wanted to capture the real Grimes, a woman who doesn't try too hard to be cool or fashionable. Her style is bold, courageous and honest. She doesn't compromise herself for anyone. There aren't many people like that. Grimes is a one-off.'

Grimes: 'I live in Los Angeles now, though I'm touring at the moment, which is an experience I would describe as confusing.It's my greatest achievement that we've figured out how to turn electronic music into a viable live show. As a multi-award-winning designer – she won British Brand of the Year at the ELLE Style Awards 2016 – a life-long vegetarian, eco-campaigner and mother to four children, there's no one better than Stella McCartney to champion positive role models. She counts actresses Gwyneth Paltrow, Kate Hudson and Liv Tyler, as well as supermodel Kate Moss, as close friends. But when she's determined to stay pals with the face of her new fragrance, Pop, and all-round 'cool-ass girl' Grimes, you get the feeling the pair will be putting the world to rights over vegan food for years to come. Here, Stella shares her admiration for the producer, pop star and artist.

'I wanted to work with Stella because she really cares about creating ethical products, and goes above and beyond to do so. The thing I most deplore in others is cruelty and violence so that's my number-one priority when considering being involved in a campaign.

'Fashion is one of the most collaborative parts of my job. Visuals are important and I think there's a fine line between creating a modern aesthetic without sexualising oneself. I don't know how to make clothes and I don't have time to go shopping, so I work with designers and my stylist, Turner. In terms of the actual modelling, I feel like it's easier than people might think. I learned everything I know from the first season of America's Next Top Model.'