"Jennette has suffered an unimaginable loss," her rep said. "Please respect her and her family's privacy at this time of mourning. She appreciates the love and support of her fans."
According an op-ed that the iCarly star wrote for the Wall Street Journal, Debra had battled breast cancer for 17 years. Though she went into remission, the cancer returned and spread to her brain in 2010.
Her boyfriend Andre Drummond tweeted Friday, "First time in my life, I don't have all the answers for something."