This is heartbreaking!

Miley Cyrus' beloved dog Floyd passed away on Tuesday, and during her concert in Boston last night, the 21-year-old singer broke down after performing a cover of "Landslide."

"It's gonna be hard for me to sing this next song. I'm not sounding myself, I don't feel myself," Cyrus told the crowd. "I'm sure you guys already know, but the reason that I'm so upset is my dog. I shouldn't say he was my favorite, but he was my favorite, and he passed away. I just want to do a song for him. We used to always listen to Fleetwood Mac together. This is his favorite song...so I wanna do this song for Floyd. This song is 'Landslide.'"

"Today is the 2nd worst day of my life," the pop star wrote on Twitter after learning that her Alaskan Klee Kai had died. "I don't wanna say it because I don't want it to be real...But my precious baby Floyd has passed away. I am broken. I know I don't mean it but I wish he would've taken me with him. This is unbearable. What am I gonna do without him? I am miserable...I'm sorry in advance if I am not myself tomorrow, Boston. I will try my best to be my best."