Former U.S. Senate Majority Leader George Mitchell of Maine speaks during a Bangor Daily News event in this 2016 file photo. He is entering treatment for leukemia this week, according to an aide at his former law firm. Credit: Ashley L. Conti / BDN

Former U.S. Sen. George Mitchell of Maine, who rose to majority leader and gained international renown for helping negotiate a peace agreement in Northern Ireland, was recently diagnosed with leukemia, according to an aide from his former law firm.

Mitchell, 87, is entering a hospital for treatment this week and he and his family declined to provide additional information about his condition, including his prognosis, the aide said on Thursday. He was treated for prostate cancer in 2007 but recovered.

A Waterville native who graduated from Bowdoin College, Mitchell was first appointed to the U.S. Senate in 1980, and served as Senate majority leader from 1989 to 1995, once declining a Supreme Court appointment. The Democrat helped broker a peace agreement in Northern Ireland in 1998 and led a blockbuster 2007 report on steroid use in professional baseball. He served as a special envoy to the Middle East under former President Barack Obama until 2011.

Mitchell had been working for a Washington-based law firm, DLA Piper, until the end of last year. There was no public announcement of his departure and his biography page is still active and calls him a “consultant,” but the aide from the firm said he retired at that time.

Last August, Mitchell was named in documents unsealed as part of a lawsuit against disgraced financier Jeffrey Epstein, who was arrested last summer on sex trafficking charges and later died by suicide in prison. A woman who alleged Epstein trafficked her as a girl said she was asked to visit Mitchell as part of a trafficking ring. Mitchell denied those allegations and said he had no knowledge of Epstein’s misconduct.

Mitchell’s public appearances have been limited over the past year, though he gave a tribute for the funeral of John Hume, an Irish politician and Nobel Peace Prize recipient who passed away earlier this month, the BBC reported.