"You make me laugh. You make me smile. You make me LOVE. You make me want to be BETTER. Speaking of, it doesn't get any BETTER than you," Timberlake captioned a sweet Instagram post before the party. "Now, I know for sure that it's BETTER to be lucky than good. Ask me who the luckiest guy in the world is and I will tell you that you are looking at him. Happy Birthday, my heart."