On a day of competition for the royals, the pair later travelled to the Roscor Youth Village charity in Co Fermanagh where Kate and William went head to head in a canoeing race on Lough Erne.
Speaking at the event, the Duke of Cambridge hailed Mary and her work to get young people involved in athletics. Asked whether the royal visitors expressed their support for the Sure Start programme, Ms Ward said "absolutely".
Middleton paired her mint-hued midi with taupe suede pumps, a matching nude clutch and casual curls, while Prince William opted for a suit sans tie.
Kate, 37, could be seen laughing as she went behind the bar and poured pints with her husband at the party.
He watched the tap with a keen eye and commented "look at that bad boy", concluding: "Perfect...good enough for an advert".
Saudi princess becomes country's first female ambassador with USA role
She had promoted greater inclusion for Saudi women in sports and breast cancer awareness, according to her official biography. Recently, the World Economic Forum appointed her to its Young Global Leaders program.
The appearance at Empire Music Hall wrapped up an action-packed day of activities.
Speaking afterwards about the visit, Kathryn Ward, a 26-year-old mother-of-two, said the Duke and Duchess had bonded with fellow parents over their mutual experience of nighttimes.
The couple arrived in Belfast this lunchtime, beginning their itinerary at Windsor Park football stadium where they heard about outreach campaigns including Ahead of the Game and Shooting Stars, run by the Irish Football Association. She took to the pitch in $120 Sweaty Betty x New Balance Fresh Foam Cruz Sneakers, paired with a $280 Barbour Longshore Quilted Jacket. Keen football fan William, 36, also came prepared with a second pair of shoes and spent much of the afternoon in Nike trainers.
Kate was also given a lesson in special effects make-up.