Blake and Gwen's relationship is Adam Levine-approved

The Voice coaches are on each other's team.

And after Blake Shelton and Gwen Stefani went public with their relationship Wednesday, Adam Levine posted a picture of him and the pair on Facebook, showing his support.

"Family. (Blake is the stepbrother)," he joked in the caption.

So can we expect Adam's vocals on one of those new country songs Blake and Gwen are writing? Since they're family and all...