Article continues below advertisementOK! can reveal King Charles is said to be "nursing secret sadness" as he prepares to mark what would have been Queen Elizabeth II's 100th birthday, with insiders suggesting the monarch is quietly reflecting on how far the royal family has shifted since her death.The 77-year-old King will lead national and Commonwealth commemorations on April 21, delivering a televised address celebrating the life and legacy of Queen Elizabeth II, who died in September 2022 at age 96.