The Fleetwood Mac star was a huge fan of the Golden Globe-winning series long before show creator Ryan Murphy decided to devote a whole episode to her band's hit album Rumours in 2011.
Nicks met the entire cast when she visited the set, and was able to watch Naya Rivera, Heather Morris and guest star Gwyneth Paltrow cover her iconic song, Landslide.
So when Nicks found out about Monteith's death from a drug overdose in July (13), she felt compelled to reach out to his heartbroken girlfriend and co-stars.
She tells Rolling Stone, "I was devastated when Cory Monteith died. I wrote a letter to the cast, and I wrote a letter to Lea Michele. I tried to be of some solace."
Nicks' friendship with Murphy and his producing partner Brad Falchuk continued behind the camera, and when they approached her to guest star on their other hit show, American Horror Story, she found the offer impossible to decline.
She explains, "I couldn't say no. I could say, 'I'm not an actress, so it's going to suck - but I will be glad to try, for you... I don't want to be bad at anything that I do that people see.
"If I try to learn to skate and I'm terrible, nobody's going to know about it. But it was really fun. I now belong to a very secret society. And you'll be surprised - not with my terrific acting, but with the whole thing."