'Tower of strength, mentor, friend... Sophie's bond with Kate is one of the monarchy's biggest strengths

WITH her 61st birthday just around the corner, Sophie the Duchess of Edinburgh's growing bond with the Princess of Wales is a sign of her soaring royal importance.

- BY ANNA POINTER

With Kate at a Christmas carol service last month Sophie and Kate have developed strong bond

Long seen as the family's secret weapon, Sophie's close affinity with Kate is now considered one of the monarchy's biggest strengths.

Former BBC royal correspondent Jennie Bond said: "They have a lot in common.

"I'm sure that Sophie was an invaluable mentor for the princess as she learned about royal ways of life.

"I think they're now much more like friends than aunt and niece, and the two of them have established a very solid friendship which will serve our future Queen well.

"Sophie is not so much a 'secret' weapon these days: she's an outright star of the royal family."

Kate, 44, is said to have called Sophie - whose birthday is on January 20 - a "tower of strength" as she battled cancer.

Jennie adds: "I'm sure it's been a comfort for the princess to know that Sophie was on hand during the last difficult couple of years. After all, Sophie had her own serious health problems with an ectopic pregnancy and a very difficult birth."