'Reacher' Star Alan Ritchson Hosts President Biden and Hunter on Set

Alan Ritchson's getting a taste of presidential shine -- and, of course, hate -- after kicking it with Joe and Hunter Biden on the set of "Reacher" and sharing it with the internet. As Julia Roberts put it ... big mistake. Huge.

The jacked-up action star is especially pumped about getting to host Prez Biden for a visit while filming his hit Prime Video series. Alan was grinning from ear to ear in a bunch of pics and videos he got with the former POTUS and his son.

He said it was a "privilege and honor to meet the Biden family. They couldn’t have been more lovely. Kind, joyful, gracious and present."

Despite his excitement, Alan got a healthy dose of political backlash in the comments, with gems like ... "Did Hunter show you how he can chase a prostitute out of a hotel room while simultaneously still smoking a crack pipe?"

Or, "Reacher season 4 - presidents son is selling secrets to foreign governments."

Maybe the best advice came from a fan who said, "I wouldn't have posted this lol" -- still, Alan didn't let IG trolls rain on his presidential parade.

He seemed to mock all the buzz about Biden's cognitive abilities, adding, "We chatted briefly about simple stuff, like string theory and quantum entanglement."