Willie Nelson has opened up about his secret family, revealing he fathered a daughter with an old flame.

In his upcoming memoirs, Roll Me Up and Smoke Me When I Die, the grizzled country legend admits he only recently learned a brief fling with "an old friend" produced a baby daughter, who has gone on to have her own family.

Nelson also discovered his lost child's daughter has also had a baby.

He writes, "Mary Haney was my old and dear friend from long ago (and it) turns out Mary and I had a child together called Renee, who has a daughter, Noelle, who has a daughter, Jordan, I am proud to call my great-granddaughter.

"Mary was a sweet lady, and I'm glad we had a family together."

Nelson also has seven children from three of his four marriages.