Imagine Dragons Singer Dan Reynolds' Wife Files for Divorce

The wife of Imagine Dragons frontman Dan Reynolds is officially divorcing him ... after the estranged couple announced their separation last year.

According to court records, Dan's wife Aja Volkman filed Tuesday in L.A., pulling the plug on a marriage that lasted over a decade. They have four kids together.

As we reported, the soon-to-be exes called it quits in September, and a couple months later Dan was linked to his new GF Minka Kelly.

We've seen them on a handful of dates since then -- from grabbing dinner to holding hands on a walk to some lunchtime PDA.

Dan's been in pretty good spirits since his split from Aja ... and not only because of Minka. We recently saw him dancing up a storm on a cruise to Mexico last month.