The Queen’s daughter will make military history by becoming the first woman to lead the Royal Marines. Nephew Harry was stripped of the prestigious post after marrying Meghan, Duchess of Sussex and moving to the United States.
The Princess Royal now holds the honorary title of Admiral in the Royal Navy.
Her new job is expected to be announced in August following official confirmation from the monarch.
The royal family has undergone a number of changes in recent years as Prince Harry and his uncle Prince Andrew have all lost their honorary military titles.
Prince Charles has also taken a leading role as the Queen, who celebrated her 96th birthday on Thursday, scales back her public appearances.
Buckingham Palace is set to announce a raft of new military appointments, including Princess Anne as head of the Marines and possibly at least two new roles in the Army.
Regiments including the Marines, Grenadier Guards, Irish Rangers and the Yorkshire Regiment were left without an honorary chief after Harry and Andrew were removed from their roles.
Anne, 70, is known for taking on a number of public engagements.
She already commands 10 regiments, including Colonel in Chief of the King’s Royal Hussars, the Royal Scots, the Gurkhas and the Royal Army Veterinary Corps.
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He said: “Princess Anne has a long history of working with the Royal Navy and would be perfect for the role.
“Harry was with us only briefly and we gave him his green beret, which worried some people, and then he had to retire.”
The Duke and Duchess of Sussex made their first public appearance together in Europe since stepping down as senior working royals at this month’s Invictus Games more than two years ago.
Harry founded the games to help rehabilitate injured or ill military members and veterans from around the world by challenging them to compete in sporting events similar to the Paralympics.
At the closing ceremony in The Hague, The Prince spoke of his pride in the competition ahead of him.
He told the audience on Friday: “You all climbed your mountain. And I couldn’t be prouder of each and every one of you.
“We, your friends and family, couldn’t be prouder of who you are and what you represent, especially considering what it takes to get here. Mindset is everything.”
He added that he found out from media interviews and conversations that had it not been for the Games, some of the participants would have taken their own lives.
Harry said: “You made a choice to be here, to stay with us, to grow with us and I can’t explain how much it means to me and how much you mean to all of us. So thanks.”
The Duke announced that the 2025 Games will be held in Vancouver and Whistler, Canada.
He said, “Ladies and gentlemen, Invictus is coming back to North America and that’s a very, very good thing.”
In 2023, the games are scheduled to take place in Düsseldorf, Germany.