Sophie, the Duchess of Edinburgh, rang in her 60th birthday by posing for an official portrait in a white Proenza Schouler coat paired with a brown turtleneck and wide-leg bright green pants. The elegant yet modern look paired with a bold splash of color–a welcome departure from the conservative power suits she wore in her early royal days–showed just how far Duchess Sophie’s style has come over the years.

Sophie, Duchess of Edinburgh turns the milestone age of 60 on Jan. 20. Here, fashion insiders, including designers of some of the royal's favorite brands, reveal the secrets of her style evolution.

Kate Middleton found a mentor in Sophie, the Duchess of Edinburgh when she was first welcomed into the royal fold, but their warm working relationship has developed into an even closer sisterly bond amid Kate’s cancer battle.