Rocker Stevie Nicks still regrets marrying her best friend's widower in the 1980s, so they could bring up her pal's baby.

The Fleetwood Mac star vowed early on in her career never to get married or have children of her own, so she could devote herself to her music, but she turned her back on that pledge in 1981 after childhood pal Robin Anderson lost her battle with cancer after giving birth to a son named Matthew.

Nicks was convinced marrying Anderson's husband Kim and bringing up her baby together was the best thing to do for the child - but the union was doomed.

The rocker admits that even now, reflecting on her life, she can't even comprehend the reasons behind her actions.

During a candid chat for Oprah Winfrey's Master Class show, which aired on Sunday (24Mar13), she explained, "Matthew was born, Robin died, and I was grief-stricken. Completely and utterly grief-stricken. I had lost the best friend I had ever had in my life and I just went on a mission because I wanted that baby (to be looked after).

"I convinced Kim, and so three months after Robin died, we got married. And I thought that's what Robin would want, somehow. And it just blew up in our faces because it was so the wrong thing to take Matthew and her husband; it was so beyond insane that, I mean, I can't even tell ya (sic) (what I was thinking)... I can't even, my own self, sitting here now, I can't even... 'What were you thinking?' You know? I wasn't thinking, so that's the story of my 'marriage'.

"That was just me in my own crazy way, trying to help. Robin was my rock; she was my best, dearest friend since I was 14 and without her I thought I'll never make it. So, of course I was going to try and take care of her baby... but you can't, you have to let things go like that. It wasn't anybody's fault."

Nicks reconciled with her stepson years later and has since established a close bond with him.