Justin Bieber I'm Nature's FineAssT

3/26/2016 7:11 PM PDT BY TMZ STAFF

0326-justin-bieber-ass-beach-photo-INSTAGRAM-01Justin Bieber just gave fans two reasons to smile ... posting a pic of his bare cheeks on Instagram.

JB put the pic up Sat. night with the caption, "Dat ass doe." It's unclear where the pic was taken, but one thing's for sure, it's breathtaking.

High-five to Mother Nature.