"He was left in a box in front of Walmart," she tweeted Wednesday. "I don't understand how people can be so cruel. That's why we named him Happy."
She followed up this tweet with another, showing a picture of the singer and her new pal getting "groomed" at a salon.
Though the puppy's new owner isn't sure of its breed, judging by its characteristics, Miley suspects it might be a Rottweiler-beagle mix. Happy will have plenty of canine company at the Cyrus residence, as Miley already has three other dogs: Lila, Floyd and Ziggy.