Kim is now proud Mummy to baby Mercy. Copyright: [Twitter/Kim Kardashian]
Kim reported the news on her Twitter page, where she posted: 'Rest in peace my little Mercy'.
Rest in peace my little Mercy bit.ly/YWfl5D
— Kim Kardashian (@KimKardashian) December 8, 2012
Kim then explained what had happened in full, saying that she is heartbroken.
The Kardashian wrote: "It is with deep sadness that I have to tell you all that my kitten, Mercy, has passed away. My heart is completely broken."
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"When I first got Mercy, I had never lived with a cat before and so I had no idea that I was allergic."
She continued: "I knew that Sydney, Khloe's assistant, who had recently lost a cat she had loved and cared for cats 17 years, would be the perfect mum for Mercy and Sydney was so excited to have Mercy as her own!"
Mercy was one of the most famous cats in celebland. Copyright: [Twitter/KimKardashian]
The star went on to explain that Mercy "got really sick" after a couple of weeks.
A visit to the vet revealed that Mercy had a rare form of stomach cancer and she died the following day.
Kim added: "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. RIP Mercy Xo."
The kitten was a present from Kim's boyfriend, Kanye West.
However, she had to be adopted by Kim's sister Khloe's assistant after it turned out Kim was allergic to her fur.
Mercy had become one of the most famous pets in celeb land and even had her own Twitter page.
We hope Kim is feeling better soon!