Prince Philip, the Duke of Edinburgh and husband of Britain’s Queen Elizabeth II, has died at age 99, according to Buckingham Palace. Prince Philip married Princess Elizabeth in 1947 and has been the longest-serving royal consort in British history.

“It is with deep sorrow that Her Majesty The Queen announces the death of her beloved husband, His Royal Highness The Prince Philip, Duke of Edinburgh,” Buckingham Palace said in a statement. “His Royal Highness passed away peacefully this morning at Windsor Castle. Further announcements will made in due course. The Royal Family join with people around the world in mourning his loss.”

Flags on landmark buildings around Britain were lowered to half-mast to mark the beginning of a period of mourning. Prince Philip, who recently celebrated his 99th birthday at Windsor Castle, is the royal family’s most notable death in recent years, following the passing of Princess Diana in 1997 and Princess Margaret’s Death in 2002. The Duke stepped down from royal engagements in May 2017 and made his final official appearance at the Royal Marines parade at Buckingham Palace that year.

Queen Elizabeth II and Prince Philip are the parents of four children, Prince Charles, Princess Anne, Prince Andrew and Prince Edward. They have eight grandchildren, including Prince William and Prince Harry, and 10 great-grandchildren.

Prince Philip has been in the pop culture spotlight in recent years with his portrayal on Netflix’s The Crown. The Duke of Edinburgh was played by Matt Smith in the first two seasons and Tobias Menzies in the two most recent seasons. Jonathan Pryce will take over the role for season five.

No official details have been released about the Duke’s funeral. According to Sky News, Prince Philip will likely have a royal ceremonial funeral rather than a state funeral, and the Queen will sign off on the plans in the coming days.