They chatted warmly as they joined Prince Albert of Monaco and his nephews Pierre and Andrea Casiraghi at the trophy presentation ceremony.
As well as their backgrounds and marrying into royalty, Charlene and Sophie have plenty of other things in common.
They've both had the experience of being in the headlines and weathering the storms that go with such attention.
Just before Charlene's wedding, the South African even commented that among the Windsors, it was Sophie – along with Prince Harry – to whom she had grown closest.
Indeed it was Sophie and the Earl of Wessex who represented the UK at Charlene and Albert's spectacular wedding ceremony.
Several other familiar faces were spotted at the racing event, which has long been a favourite of the stars.
In the past, the likes of J-Lo, Brad Pitt and Michael Douglas have all been spotted mingling with royalty and checking out the racing cars in the pitt lanes.
This year Antonio Banderas, Will Smith and Eric Clapton were on hand.
Later on the royal ladies changed into evening gowns for a glittering reception. Charlene, who sparkled in a pretty dress with a sequinned top and long black skirt, was seated next to the Grand Prix winner Mark Webber.
Sophie, meanwhile, looked beautiful in a one-shoulder pink creation.
All the news as Duchess Kate's due date draws close...