Liz Buttle, 60, said she had not taken precautions against pregnancy because she thought she had gone through the menopause.
But a "strange feeling" in her stomach made her joke with her lover, Pete Rawstron, 58, that she could be expecting and a home pregnancy kit confirmed it.
Ms Buttle told the News of the World yesterday: "I thought, 'Oh yes, oh no... oh dear!' But I coped."
Baby Joe was born on 20 November weighing 6lb 15 oz but his birth only became known to the world outside his home in Cwmann, Dyfed, last week.
Describing the moment when she cradled him in her arms, Ms Buttle told the newspaper: "I was presented with my perfect baby. I held him and didn't regret a thing."
Liz Buttle runs her own small farmhold which has no hot water and a flush toilet only in the garden. For the last year she has shared her life with Mr Rawstron, whom she met when he delivered hay to her farm.
This weekend, it was announced he had returned to his wife of 38 years, Vera, although he intends to keep in touch.
He was reportedly surprised to discover his son's mother was 60, as were the staff at the West Wales Hospital in Carmarthen where she gave birth.
She has no fears about bringing up a baby at her age. "I don't think age has anything to do with it. As an older mother, I'll have more patience, time and wisdom to give my son." Ms Buttle said she was still fit enough to move sacks of cattle feed and added: "Thousands of children a week are born to parents who don't or can't give a damn. I never considered aborting my baby and I intend to be there for him."
Ms Buttle, a widow whose second husband died six years ago, is believed to the oldest woman in the world to give birth naturally. She would also appear to hold the world record for the longest gap between her first and second child. Belinda, her daughter, is 41.
A 63-year-old Californian woman lied about her age to get fertility treatment and gave birth in 1996. Rosanna Della Corte, an Italian, had a baby in 1994, following an egg implant.Reuse content