Video: Miley Cyrus Breaks Down Over Dog's Death During Performance

The singer is still mourning the death of her Alaskan Klee Kai puppy Floyd, who passed away on Tuesday -- and the pooch was still on her mind during a performance in Boston earlier today.

The singer invited thousands of fans to a special KISS 108 FM sound check before her Bangerz tour in the Massachusetts capitol city later on this evening, where she dedicated "Landslide" to her late pet.

"My dog who is, I shouldn't say he was my favorite, but he was my favorite, he passed away," she told the crowd. "I just wanted to do this song for him because we used to always listen to Fleetwood Mac together and this was his favorite song."

Miley was visibly upset during the performance, and, at one point, even started crying. Her sister Noah even came onstage to comfort Cyrus, giving her a hug and moral support while she sang (below).

The 21 year old has been tweeting non-stop about Floyd since last night, calling today "the 3rd worst day in my life," and adding "I am beyond miserable."

Cyrus has already apologized in advance of tonight's show, promising her Boston fans that she will "try my best to be my best."

Read more of her tweets below.