Published Monday, 07 November 2011
Dr Hegarty sent a letter to priests on Monday morning, stating he will step aside for health reasons.
"In July of this year, a local newspaper indicated that I had been undergoing medical tests," the letter said.
"At the time, I stated that, while this was accurate, I had not received any diagnosis or treatment.
"However, very recently, I received a diagnosis of a condition which is, unfortunately, irreversible and progressive. I am now receiving treatment for this condition."
The 71-year-old became Bishop of Derry in 1994, after serving in Raphoe for 12 years.
Bishop Emeritus of Derry, Edward Daly said he was "shocked" by the resignation.
"I was aware that he had been in indifferent health for some time. I am conscious of the huge and demanding burden of responsibility that a bishop has to accept," he said.
"Bishop Hegarty was prudent and wise to submit his resignation if he did not feel able any longer to continue in his episcopal responsibility."
Michael Kelly, Deputy Editor of the Irish Catholic, said: "It will be the fourth Irish diocese to be vacant with three other bishops already past retirement age and awaiting a successor.
"In total, Pope Benedict will shortly have to decide whether to appoint seven new bishops or amalgamate dioceses," he added.