Mollie was grinning from ear to ear inside the party, where she met up with Gandy after they avoided being photographed together on arrival.
The 31-year-old model was dapper as always grey suit and open-necked blue shirt.
Mollie and her Essex-born beau - now one of the highest-paid models in the country - met at a party in March, and have been quietly dating ever since.
The singer split from ex-boyfriend Andy Brown in early 2011. Gandy, who became a household name for the Dolce & Gabbana advertisement showing him in a tiny pair of white pants, has been linked with Lily Cole and Lindsay Lohan.
They made an effort not to be photographed together at events early on, but made their debut as a couple at a Ralph Lauren gala dinner in Paris a fortnight ago, after they were spotted enjoying a romantic stroll through London the same week.
Mollie hinted at what she was looking for in a partner in a Glamour magazine interview, conducted before the romance went public.
She said: ‘I love an old-school gentleman. Picking me up for dates, sending flowers, holding the door open, I love it all. I think a man should treat you like a princess.’