The couple, who have been dating for two years, got glammed up for the occasion - and they've never looked so loved up.
James, 27, arrived suited and booted for the charity event at the Park Lane Hotel while his millionaire TV presenter girlfriend looked lovely in a pale blue lace dress by NEVENA London paired with contrasting tomato red shoes and a clutch bag.
Donna, 35, wasn't the only belle of the ball, though. The pair partied with the Duchess of Cambridge's younger sister Pippa and her long-term boyfriend Nico Jackson, along with The Saturdays star Mollie King.
Pippa was radiant in a LRD (that's little red dress) teamed with matching accessories. Mollie took on the plunging neckline trend in a floor-sweeping sheer black gown.
Recent reports suggest James and Donna will beat Pippa and Nico to marriage.
After Donna was photographed wearing a very sparkly rock on her engagement finger in 2013, it sparked speculation that Kate's younger brother might have popped the question.
Although the gossip was quickly laid to rest by the couple, Donna revealed she isn't one to shy away from marriage.
"I've never been married so maybe one day I will do the wife thing," she told the Telegraph at an event in London's Mayfair last summer.
Are those wedding bells we hear?
See more of the future Mrs Middleton's glamorous style below...