Penelope Bradbourne, 67, also known as Countess Mountbatten of Burma, was one of Prince Philip's closest friends later in life after he taught her carriage driving in the mid-1990s.
Penelope was such a trusted friend that in recent years she was given the nickname "And Also" by royal aides as she was invited to so many events that Philip was due to appear at, according to the Daily Mail.
Now, Penelope 'Penny' Knatchbull, previously known as Lady Romsey and later Lady Brabourne, will be one of the 30 people allowed to attend his funeral and the only person in attendance who is not a direct blood relation of the Duke or someone who is married to a blood relation.
This is a sign of how close Penelope was with the Duke that she will join the Queen, as well as her four children, eight grandchildren and their spouses.
The mourners include Prince Harry, Prince William and his wife Kate, and the four children of the Queen and the duke, Prince Charles, Princess Anne, Prince Andrew and Prince Edward.
Princess Anne's husband, Vice Admiral Sir Tim Laurence will walk in the procession behind Prince Philip's coffin.
The duke's other grandchildren and some of their spouses will be there - including Peter Phillips, Princesses Eugenie and Beatrice, and Zara and Mike Tindall.
Jack Brooksbank and Edoardo Mapelli Mozzi, married to Eugenie and Beatrice respectively will attend.
Several of the Queen's cousins have been invited but without their spouses, including the Dukes of Kent and Gloucester. Princess Alexandra will also be alone, as she is a widow.
The late Princess Margaret's daughter, Lady Sarah and her husband, Daniel Chatto will be there, along with Margaret's son, The Earl of Snowdon.
There will also be three members of Philip's German family, Prince Phillipp, Prince Donatus and Prince Bernhard.
Much of Philip's German family were denied a place at the Queen and Prince Philip's wedding due to the anti-German sentiment after the second war.
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