Kim Kardashian on September 16, 2012 in Miami, Florida. Credit:

Kim Kardashian is in mourning.

Her adorable kitten Mercy -- a gift from boyfriend Kanye West -- has died, Us Weekly confirms.

"Kim is so sad [about losing Mercy]," a source close to the reality star tells Us.

E! News reports that the fluffy feline passed away from a "cancer-like virus often associated with breeding," and that Kardashian, 32, had given the cat to sister Khloe's assistant Sydney after discovering she was allergic. (At the time, Sydney was grieving the loss of her own pet cat, who had passed away after 12 years.)

According to E!, Mercy's new owner decided to have her euthanized after learning that her kitten was terminally ill, and that "even aggressive treatment" wouldn't help her situation.

Kardashian first showed off the newest Kardashian on Instagram in early September. She named her pet after one of boyfriend West's summer hits, "Mercy."