Soul singer Natalie Cole has been diagnosed with hepatitis C. The star - daughter of the late Nat King Cole - was forced to pull out of a performance in California last week , citing illness. And now Cole's representative has confirmed that she has been struck down by the chronic liver disease. The condition was revealed during a routine examination and is likely to have been caused by Cole's excessive drug use throughout the 1980s. Dr. Graham Woolf from Los Angeles' UCLA/Cedars-Sinai Medical Center, who has been treating the Grammy winner, insists she has a good chance of making a full recovery. He says, "She has had a terrific response to her medication and is now virus negative. This gives her an increased chance of cure. But, she has also suffered significant side effects from the anti-viral medicine. Her side effects include fatigue, muscle aches and dehydration but she is recovering from these." And Cole has vowed to fight illness, saying, "I am embraced by the love and support of my family and friends; I am committed to my belief in myself and in my abiding faith to meet this challenge with a heartfelt optimism and determination."