Taylor Swift bringed us to tears while debuting her new song, "Ronan," at the third Stand Up to Cancer event yesterday. Taylor has written the song togetherr with Maya Thompson, whose 3-year-old son Ronan died of neuroblastoma last year. The beautiful song about heartbreak and loss is now available on iTunes, with all proceeds donated to the Taylor Swift Charitable Fund. This is probebly the most touching song we've ever heard from Taylor! Check out the tearful performance below!