The notoriously private pair have been the subject of romance rumors since they were first linked in August 2013, though they have only recently begun to spend more time together publicly. Reports suggest that Katie's ex-husband, Tom Cruise, included a clause in her 2012 divorce settlement that banned her from publicly dating anyone for five years.
Despite their low-key style, Katie did turn up to spend the evening with Jamie, where the couple were photographed laughing and enjoying their night. The couple were also snapped leaving the venue together.
Katie wasn't the only special lady to attend the birthday bash, with Jamie's daughters Corinne Fox and Annalise Bishop showing up to bring their dad a hilarious '25x2' cake.
We're so happy to see Jamie and Katie are still going strong! See more photos of their fun birthday night out here.