When the 20 year-old powered to victory in the 200m butterfly final race, the royal leapt out of her seat, screaming and crying.
With her husband Prince Albert looking on as her countryman was crowned king of the podium, Charlene also kissed the medal.
Charlene, a former Olympic swimmer herself, knows only too well the determination it took for Chad to triumph over his "hero" Michael Phelps. The American is widely regarded as the best Olympic swimmer alive today, with a plethora of medals to his name.
But on this occasion, he had to make do with silver whilst his young competitor and his royal fan rode the wave of success in the Aquatics Centre.