Some random dude in Nashville got on one knee to propose to his girlfriend ... and none other than NFL Pro Bowl tight end Greg Olsen was there to capture the whole thing on his phone!!!
Now, the Carolina Panthers star didn't know the couple before the magical moment ... but that didn't keep him from absolutely losing it with excitement when he finds out the girlfriend said "YES."
"Did she say yes??" Olsen asks ... "I got it on video, dude. I'm gonna send it to you!!"
The whole thing is kinda funny -- you can tell the future groom is super excited about the engagement ... but seems a little confused about why this 6'6", 255-pound man is shooting the whole thing.
Don't worry, after some celebratory kissing with his wife-to-be ... the dude seems grateful Olsen got the whole thing on video ... saying "oh my God, you're my hero!"
"This is the best thing I've ever witnessed," Greg told the couple ... "Dude, I am so sending this to you!!!"
Olsen explained why he whipped out his phone and captured it ... saying "I wish I had my engagement on video, so I pull my phone out and capture it. Glad I did even though I didn’t know who they were!"
"Congrats and wish you a lifetime of happiness!! #random"