David Muir had fans delighted with his latest social media post, as he took to sharing a personal and heartfelt tribute to a friend.MORE: David Muir and Kelly Ripa have the sweetest friendship: all the detailsThe Good Morning America anchor posted a throwback shot of himself with close friend and fellow TV personality Kelly Ripa.The shot showed both of them with their backs turned to the camera as they walked arm in arm, and he wrote on the picture: "Gratitude.