Carol Ann Susi, who played the role of Howard's mother Mrs. Wolowitz, died after a brief battle with an aggressive cancer. She was 62.
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After hearing the tragic news, co-stars Kaley Cuoco-Sweeting, Mayim Bialik, Kunal Nayyar and Melissa Rauch each took to social media to remember their beloved friend and colleague.
Posting a black and white photo of Susi on her Facebook page, Kaley wrote:, "Rest in peace hilarious, adorable, sweet Carol Ann Susi.
"You will forever be part the Big Bang Theory family."
Kunal Nayyar, who plays Raj, one of Howard's friends, added: "My heart is broken.
"I will miss your smile. Your spirit is forever with us."
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Big Bang Theory producers released a statement yesterday mourning the loss of Carol, whose husky, overbearing voice was a big part of the show.
They wrote: "The Big Bang Theory family has lost a beloved member today.
"Unseen by viewers, the Mrs. Wolowitz character became a bit of a mystery throughout the show's eight seasons.
"What was not a mystery, however, was Carol Ann's immense talent and comedic timing, which were on display during each unforgettable appearance."
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They added: "In addition to her talent, Carol Ann was a constant source of joy and kindness to all. Our thoughts and deepest condolences are with her family during this time, and we will miss her greatly."
Our thoughts are with her friends and family at this sad time.