The couple tied the knot on Labor Day, according to their marriage certificate, and the singer-songwriter and the "Stranger Things" star shared a few pics of their ceremony from the Graceland Wedding Chapel. Classic!

The lovebirds look totally smitten and full of joy inside the chapel -- with Elvis singing away -- and outside on a Vegas street as Lily showed off her vintage white wedding dress and veil.

Apparently, a day full of love and marriage in Sin City works up your appetite ... Lily and the fam chowed down on some In-N-Out after the nuptials.

We broke the story ... David and Lily obtained a marriage license Sunday in Vegas, the first indication they were about to seal the deal.

Up until recently, they've been very private about being together -- with Lily revealing their engagement via a selfie back in May -- but they're letting it all out now.

David even pointed out that wildfires ravaging California and a pandemic affecting the whole world couldn't stop them from becoming husband and wife.