On Monday, October 28, the 44-year-old star of Netflix's hit series shared a photo of himself and Allen, 34, at Disney's Magic Kingdom dressed in costume.
"The prince, princess and the parking lot," Harbour, 44, captioned the sweet snap.
"That seven dwarves mine ride is the best one in the whole damn park," he continued. "Go on, fight me."
Harbour was dressed in a royal blue and gold cape, while Allen wore a pink and purple princess dress. The photo was snapped in a parking lot mirror while the singer looked down, inspecting her shoes.
The pair went public with their rumoured romance earlier this month by packing on the PDA during a weekend stroll around New York, with David pulling the mother-of-two in for a number of kisses and grinning as he lavished her with attention.
And during Harbour's "Saturday Night Live" hosting gig, Allen posted a number of snaps of him on her Instagram Stories, with the caption, "Mine."
The "Smile" singer also posted a photo from a recent trip to Disney World, without Harbour, featuring "Star Wars" icon Chewbacca.