Speaking to Town&Country, Ms Naylor-Leyland said: “I think with the Queen, it was a sort of a typical teenage friendship, and they would laugh and giggle and enjoy each other’s company and didn’t discuss anything too serious.
“Princess Margaret was the sort of naughty one. And I think Alathea adored her, really, and admired her spirit.
“And, unwittingly, she often wishes that Lilibet, as she was called at the time, had more of her sister’s spark, but, of course, we all know that it’s extremely lucky that she didn’t and that she was a much more steady character.”
The book serves a dual purpose as a historical document and a set of evocative accounts that offer new insight into the Royal Family.
Ms Howard met the Queen and her sister when she moved to Windsor Great Park to live with her grandfather at Cumberland Lodge during the war years.
Ms Howard was the eldest of the three girls and had a very close “sisterly” relationship with a young Elizabeth and Margaret.
In excerpts from the diary, Ms Howard fondly refers to the Queen and Margaret by their nicknames, Lilibet (L) and M respectively and the King and Queen as K and Q.
“Monty asked me if I had one and in the end, I told them it was Robert Cecil, which amused L. M said she was so glad I had a ‘beau’! We all laughed terribly. L says she cuts photos out of the paper!
“I must say she is far more grown-up than I was two years ago. When I left, Lilibet said: ‘We part today the wiser for two secrets’ and I biked home feeling very happy and also proud at being let into such a great secret, which I shall never betray.”