Kate Middleton -- Post Baby Bump, Set ... SMOKING HOT

Kate Middleton allegedly had a baby 3 months ago -- but there is zero proof of that in these pics of the Duchess of Cambridge flashing her royal midriff all over a volleyball court.

Prince William's wife showed up for a public appearance in London yesterday, sporting wedge heels, and a banging bod that made everyone forget she was ever pregnant.

Kate gave birth on July 22 to Prince George ... and obviously hit the gym on July 23.

Women ... begin hating. Guys ... continue wishing you were Prince William.