Riley Strain’s disappearance and subsequent death captured the nation’s attention — and now we finally know how he died … as we’ve obtained his autopsy report.

According to the docs … Riley’s official cause of death is listed as drowning and ethanol intoxication — with the manner cited as accidental. There’s more info here as well … including what his BAC was when his body was examined … officials say a concentration of 0.228.

One other thing that his family might be interested in … the autopsy report notes there was no evidence of significant trauma to his body. There were traces of THC found in his system as well.

The doc also goes on to point out Riley’s body was found in the Cumberland River there in Nashville — and he was discovered by an employee at a concrete plant on March 22 … several days after he disappeared.

This brings much-needed closure for his grieving family after months of searching for answers over his untimely end.

As we’ve reported … the college student was found dead in Nashville’s Cumberland River 2 weeks after he vanished, having been kicked out of Luke’s 32 Bridge — a bar owned by Luke Bryan — for apparently being too intoxicated.

As you know, questions were raised over the nature of Riley’s death because he didn’t have his cowboy boots, pants or wallet on him when his body was pulled from the river — everything he was wearing on the night he vanished, according to family spokesperson, Chris Dingman.

Riley’s parents even speculated in an April interview his drink may’ve been spiked.

On top of that, a prelim report confirmed the absence of water in his lungs, fueling concerns he might’ve already been dead before hitting the water — casting doubt on the initial assumption he drowned.

Unsatisfied with the findings, Riley’s parents took matters into their own hands and ordered a second private autopsy from an independent company — and here’s hoping the official results can bring them the closure they seek.

Riley was only 22.