And those who speculated that the former Olympic swimmer's presence at such a high profile event was significant were proved right by the announcement that the couple are to wed.
This week's happy news is the beginning of the next chapter for the pretty South African and 52-year-old Albert, who has gradually introduced Charlene into public life over the course of their four-year courtship.
There was huge excitement when the pair were first pictured together in 2006, at the Winter Olympics in Turin. Shortly after, Albert introduced Charlene to the Monaco establishment when she was his guest at a gala Formula One event.
With each passing year, Charlene has become a more permanent fixture at royal events, looking more groomed and comfortable in the spotlight.
And the 32-year-old has been welcomed into the fold by Albert's sisters Princesses Caroline and Stephanie, whom she has been pictured alongside on many occasions.
Engagement rumours have been constant from the start. With their mutual love of sport – Charlene competed in the South Africa relay team in the 2000 Summer Olympics, while Albert is a former member of Monaco's Olympic Bobsleigh team – and their obvious delight in each other's company, the two were clearly a good match.
But while the world waited for the next princess of Monaco to be introduced, Albert took things at his own pace, despite mounting pressure for him to marry and produce an heir.
And perhaps mindful of failed marriages in his family – Caroline has wed three times while Stephanie is twice-married – it would be perfectly understandable for the principality ruler not to want to rush things.
Just last year Albert said: "You follow your instincts and your own path. You go down that path until you see a future with someone."
And it would seem that that point has now arrived.