A royal insider told The Sun: “The Queen likes to be completely calm before church and she finds Sophie’s presence soothing.”
They added: “She is trusted and relied on by the Queen in a way I couldn’t say applied to the Duchess of Cambridge or the Duchess of Cornwall.
“She is like another daughter to Her Majesty, they are that close.”
Sophie and Prince Edward, the Queen's youngest child, first met in 1993 in London at a charity tennis match organised by the Prince, and began dating shortly after.
They were married on June 19, 1999 at St George's Chapel, Windsor.
They now have two children, Lady Louise Windsor, 15, and James, Viscount Severn, 11, who is the youngest grandchild of Queen Elizabeth.
The Queen is said to be such a fan of Sophie, that she advised Meghan Markle to lean on Sophie as a mentor and ally when she joined the royal family
A source told Grazia: “The Queen likes the idea of Sophie being an unofficial mentor to Meghan.
“Sophie is often at Windsor taking the kids riding on the Queen’s horses and playing at the castle. It’s a quiet lifestyle, very much the kind Harry and Meghan want for their little one.”