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.

It’s a milestone birthday for Duchess Sophie, who officially rang in the special day on January 20 with a little more pomp and circumstance than usual, courtesy of an official new portrait and plans for a major birthday celebration at their Berkshire home Bagshot Park.

Sophie, the Duchess of Edinburgh is marking a milestone birthday! She turned 60 on Monday, Jan. 20, and friends and former colleagues have been honoring her contribution to the royal family – amid the release of the duchess' stunning new portrait.

Along with The King and Queen Camilla, Prince William and Princess Kate, who share a close bond with the Edinburghs, are said to be joining the festivities. The Princess of Wales and Duchess of Edinburgh are said to have a particularly strong relationship, with Kate viewing Sophie as a sort of "royal sister."

Photographer Christina Ebenezer also shared her favorite part of the photo shoot Sophie, the Duchess of Edinburgh is starring in a new portrait for her 60th birthday, and the photographer behind the camera is sharing an unseen snap from the photo session.

Sophie, the Duchess of Edinburgh is turning 60 in style. The royal—who marked her milestone birthday on Monday, January 20—released a trio of stunning portraits to commemorate the special occasion over the weekend that seemingly included a subtle sartorial nod to her grand new title.