Almost the moment I learned of Joan Rivers' death today, my mind wandered to this heartwarming interview she conducted with children's TV pioneer Fred “Mister” Rogers in 1983 during one of her many guest-hosting stints on “The Tonight Show.” I love it because it shows a side of Joan we so rarely got to see – wide-eyed, and tender, and deeply vulnerable. Just try not to tear up when he sings to her (beginning at 6:10). It's a beautiful moment.