The Obama fam are mourning the loss of their dog, Bo. On Saturday, Michelle Obama took to Instagram to reveal the heartbreaking news that their pup had passed away after battling cancer. The former First Lady wrote: "This afternoon was a difficult one for our family. We said goodbye to our best friend - our dog, Bo - after a battle with cancer. On the campaign trail in 2008, we promised our daughters that we would get a puppy after the election. At the time, Bo was supposed to be a companion for the girls. We had no idea how much he would mean to all of us." Related: YouTuber Nikki . . .