Charles Manson has been battling an illness for some time inside a California penitentiary – and was first rushed to a hospital off prison grounds months ago, The Post has learned.

“He’s been getting treatment at that hospital for a while. I was told months ago they removed him from the prison for an undisclosed illness,” a Corrections Department official told The Post on Wednesday.

“He’s 82, man. He was the guy who said he’s going to live forever, but I never believed it,” the source added.

The Los Angeles Times and TMZ reported Tuesday that Manson was suffering from a serious illness stemming from gastrointestinal issues.

The infamous cult leader was taken to a hospital in Bakersfield about 60 miles from his lockdown in Corcoran, sources told The Post.

Manson was convicted for masterminding the August 1969 murders of seven people, including pregnant actress Sharon Tate, and two other people on separate occasions.

He is serving a life sentence with the possibility of parole. His next parole hearing is slated for 2027 when he will be 92.