It's a sad day for Kim Kardashian.

Sources confirm to E! News that her beloved cat, Mercy, died due to a cancer-like virus often associated with breeding.

Kim K's teacup Persian kitten was a gift from boyfriend Kanye West -- but after discovering she was allergic, Kim gave Mercy to sister Khloe's assistant, Sydney Hitchcock. Hitchcock recently lost her cat of 12 years.

"It is with deep sadness that I have to tell you all that my kitten, Mercy, has passed away," Kim wrote on her blog Dec. 7. "My heart is completely broken."

Although Mercy showed no signs of illness, E! News learned that on Nov. 26 Hitchcock's boyfriend called to tell her Mercy was limp and not moving. They rushed her to an animal hospital where veterinarians made the terrible diagnosis -- a fatal virus, which acts like a cancer, had attacked Mercy's stomach.

Since even aggressive treatment wouldn't help the kitten, Hitchcock decided to have her euthanized.

"It broke not only my heart that little Mercy died at only four months old, but Sydney's too," Kim wrote. "Mercy was a gentle and loving kitten and we are all going to miss her so much. Thanks to Sydney for making Mercy's short life one filled with love."

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  • <a href="https://twitter.com/KardashianKat/status/247811645735325696">Can you tell I hate this? And bright pink? Have mercy.</a>

  • <a href="https://twitter.com/KardashianKat/status/250645297414414336">Do I need to get tested now? Have mercy.</a>

  • <a href="https://twitter.com/KardashianKat/status/250650583206359040">Someone, anyone, help me. I'm not an accessory.</a>

  • <a href="https://twitter.com/KardashianKat/status/250645297414414336">Siri, Kill me. </a>

  • <a href="https://twitter.com/KardashianKat/status/250646338486796288">She Googles herself all day long. smh. </a>

  • <a href="https://twitter.com/i/#!/KardashianKat/media/slideshow?url=http%3A%2F%2Finstagram.com%2Fp%2FPsWJn3OSwX%2F">Stop following me.</a>