Catherine, Duchess of Cambridge went super casual as she was spotted out in London December 4th with four month old baby Prince George.

The style icon looked super sporty as she rocked a baseball cap while she took a stroll with the third heir to the throne.

According to Hollywood Life, Kate Middleton swapped her royal clothes and bejeweled tiara for an everyday look.

Prince William's wife took their son for a walk in Kensington Gardens to enjoy the lovely weather before switching it up for a night of glam at the "Mandela: Long Walk To Freedom" movie premiere with her husband.

Middleton flaunted her continuously shrinking post baby body in a pair of skinny jeans as she took in the beautiful fall scenery on the palace property's gardens.

The family of three's dog, Lupo even came out with Middleton and the baby to enjoy the fresh air. The Duchess opted for a pair of sneakers as she pulled her hair back into a loose ponytail to fit under her baseball cap.

However, the quick outing wasn't all that simple and casual seeing as Kate Middleton pushed baby Prince George around in his luxurious Sliver Cross Sleepover Elegance Stroller, which retails for $2,300.

The stroller converts from a newborn carriage to a toddler stroller and is useful when it comes time to strap the baby into the car seat.

To check out the photo from Catherine Duchess of Cambridge's casual stroll with baby Prince George click HERE.