David Bowie passed away at the age of 69 on Sunday after an 18-month battle with cancer. Ever since the sad news was revealed, there has been an outpouring of sentimental messages and touching tributes on social media. In the seven hours following the devastating announcement on David's Twitter account, over 4.3 million tweets were written about him, from fans and stars all around the world, including Paul McCartney, Kanye West, Madonna, and David's wife, Iman. His son, Duncan Jones, also penned a heartbreaking note, writing, "Very sorry and sad to say it's true. I'll be offline for a while. Love to all," along with a sweet childhood photo of him and his dad. We've rounded up the most heartfelt reactions from Twitter — keep reading to see them now.