KodiakBeer
member
"Monster Quest" did a thing on big bears and they documented the other griz/polar cross shot by an Inuit in Alaska with a .223.
That one wasn't a griz/polar cross, just a polar bear well south of its normal range.
Just a few years ago, a tourist took a picture of a polar bear on the Kenai peninsula in south central Alaska. They didn't know it was unusual until showing the picture to people back home. It was sent up to AK F&G who confirmed it was an actual polar bear some 500 miles south of its normal range.
Polar bears and grizzlies have always interbred. It's just that until recently, nobody could do DNA testing to prove it.
Interestingly, the brown bears in SE Alaska (900 miles south of the nearest polar bear) are more closely related to polar bears than to other brown/grizzlies. http://www.gi.alaska.edu/ScienceForum/ASF13/1314.html
Figure that one out...