Cindy Crawford says speaking to Princess Diana was like "talking to a girlfriend".

Cindy Crawford

Cindy Crawford

The 51-year-old supermodel paid tribute to the late Princess of Wales - who passed away 20 years ago yesterday (31.08.17) - admitting she was a "class act", and recalled the late royal once rang her personally to arrange a surprise visit for Prince William and Prince Harry.

In a post on Instagram, complete with a picture of herself standing next to Diana, Cindy wrote: "Remembering this inspiring woman today. This photo was taken at Kensington Palace. Princess Diana had somehow got the number to my office and called herself to ask for me. My assistant was in shock! We finally connected and she asked if the next time I was in London I would come by for tea -- I think Prince William was just starting to notice models and she thought it would be a cute surprise for him and Prince Harry. I was nervous and didn't know what to wear, but remember as soon as she came into the room and we started talking, it was like talking to a girlfriend. She was a class act and showed us all what a modern day princess should be. Rest In Peace #PrincessDiana. #TBT (sic)"

William recently revealed his mother invited Cindy, Christy Turlington and Naomi Campbell round for tea one day as a surprise - and he was left red-faced because he had posters of the three supermodels on his wall.

He said: "She organised when I came home from school to have Cindy Crawford, Christy Turlington and Naomi Campbell waiting at the top of the stairs, I was probably a 12 or 13-year-old boy who had posters of them on his wall.

"I went bright red, and didn't know quite what to say and sort of fumbled and I think pretty much fell down the stairs on the way up. I was completely and utterly awestruck. That was a very funny memory that's lived with me forever."