The couple have been the subject of engagement rumours, but Eugenie and Jack put the speculation behind them as they attended the Serpentine party in South Kensington.
Eugenie, who works as an associate director at an art gallery, beat the chill in a black military style coat. She and her beau were pictured enjoying an evening at Albert's Club, a new venue located a stone's throw away from Eugenie's home.
Jack Brooksbank and Princess Eugenie have been together for six years
While Eugenie will have mingled with fellow guests from the art world, Jack, a nightclub manager, will have been eager to check out the new opening that boasts a whisky and martini bar, a fine dining space and a dancefloor.
Eugenie, 26, and her long-term boyfriend Jack recently spent a long weekend at Balmoral where they visited Eugenie's grandmother the Queen.
Jack has briefly met the 90-year-old monarch before but the invitation to stay for a prolonged period of time at Balmoral – one of the Queen's favourite retreats – was a sign of Jack and Eugenie's solid relationship.
The 26-year-old has been the subject of engagement rumours
The couple timed their trip with Prince Harry's 32nd birthday party – a shooting outing in the grounds of Balmoral with Harry's friends and family members.
While reports have claimed that Jack will pop the question by the end of the year, a spokesperson for Eugenie's mother Sarah, the Duchess of York, denied the claims.
"The story is not true", the spokesman told HELLO! in August.