This is how Kate Middleton showed her respect to the Queen with her latest outfit

On Tuesday, the Queen and the Duchess of Cambridge almost brought London to a standstill, as they paired up on a visit to King's College, London. The royal duo opened Bush House, which is the latest education and learning facility on the Strand Campus. Prince William's wife Kate looked her typically stunning self, wowing crowds in a gorgeous grey coat dress by Catherine Walker with a black waist belt, a black hat by Lock& Co. and black high heels by Gianvito Rossi. We have discovered that Kate's classic outfit would have taken a lot of thought - because she wanted to respect the monarch through her look. Kate opted for black tights and a hat, and according to Debrett's Spokesperson Adam Partridge, this is quite deliberate.

© Photo: Getty Images

Kate wore her tights and a hat on her outing with the Queen

"Opting to wear black tights rather than her preferred sheer ones, as well as choosing to wear a hat (not something that's normally part of her outfit), are two ways that the Duchess of Cambridge signalled deference to both the Queen and tradition during this particular engagement. One other important thing to note is Kate’s light grey dress, which allowed the Queen's pink pastel outfit to take centre stage." Later when Kate headed to the  Foundling Museum without HRH, she removed her hat for a slightly more relaxed look.

© Photo: Getty Images

Later in the day at a solo engagement, Kate removed her hat

The Countess of Wessex spilled the beans on why her mother in-law often sports all the shades of the rainbow.

MORE: Royal fashion faux pas! Fashion mishaps from Meghan Markle to Kate Middleton

In the Smithsonian Channel documentary "The Queen at 90" Sophie said: "She needs to stand out for people to be able to say 'I saw the queen'." The mother-of-two added: "Don't forget that when she turns up somewhere, the crowds are two, three, four, 10, 15 deep, and someone wants to be able to say they saw a bit of the Queen's hat as she went past."

READ: Kate Middleton's favourite discontinued beauty product is back - and we're SO excited