The 23-year-old "Confident" singer posted a cute pic the happy couple cuddling in bed, which she captioned "6" alongside a heart.
The photo of the Lovato and her 35-year-old boyfriend laying together is reminiscent of the couple's back-and-forth series of "sleeping selfies" the two shared of one another over the past few months – only this time they were both awake.
In further celebration of their big day, Lovato also posted a series of photos taken of the couple over the past six years, serving as a retrospective of their relationship.
Lovato and Valderrama have been celebrating 2016 with enthusiasm. First, they rang in the New Year together in Times Square, where Lovato performed. Valderrama snapped a cute pic with his ladylove in the middle of the dense crowd of excited revelers.
Then the couple hit the snow for a romantic getaway in a winter wonderland. Lovato shared this cute attempt at PDA while the two were bundled up against the frigid weather.
"When to try to kiss bae but it's too f**king cold to take your s**t off #snowcute " Lovato captioned the pic.
Congrats on the emotional milestone!