The Queen shows no sign of slowing down at the age of 93, as she hosted President Trump for the state visit, attended the 75th anniversary of the D-Day landings and Trooping the Colour last week.
Royal biographer Angela Levin says that while Her Majesty has made a pledge to serve her country, she looked lonely without her husband the Duke of Edinburgh by her side.
She tells Yahoo UK's 'The Royal Box:' "I think she made this pledge that she would serve her country until she died and she’s just going to keep it.
"She looks amazingly healthy, she’s very articulate, she’s very energetic, she stands up for an hour.
"I felt a little sorry for her when she was in her coach, because she was entirely on her own.
"Quite understandable that Prince Philip didn’t come at nearly 98 but it was quite lonely and I thought, this is the loneliness of the monarch."
Former royal editor Duncan Larcombe says: "That is why a lot of people think that perhaps she might stand down once her husband the Duke of Edinburgh passes away. That is certainly a possibility."