McCartney, 40, met the Umbrella hitmaker two years ago and are now thinking of collaborating on a fashion range. "They have been having regular chats," showbizspy.com quoted a source as saying.
"They call them 'mood calls'. Stella rings Rihanna and asks her to explain what has influenced her mood that day - colours, textures, patterns. Stella feels she needs to tap into a younger generation and Rihanna is happy to help. It's a bizarre way to create a fashion line but they work well together," the source added.