"I remember telling her I admire women in a different way," she tells Paper Magazine in a new interview.
"And she asked me what that meant. And I said, I love them. I love them like I love boys."
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Miley says she considers Tish and her famous dad, Billy Ray Cyrus, "conservative-ass motherf***ers," so her announcement was not taken lightly.
"And it was so hard for her to understand," Miley continues. "She didn't want me to be judged and she didn't want me to go to hell. But she believes in me more than she believes in any god. I just asked for her to accept me. And she has."
Miley, who was once engaged to actor Liam Hemsworth and dated Patrick Schwarzenegger until May, shared last month that her romantic relationships have included women as well as men.
The Wrecking Ball singer tells Paper that she's had romances just as notable with women as those she's had with her famous boyfriends.
"I've had that," she says. "But people never really looked at it, and I never brought it into the spotlight."
Now, Miley's feelings about gender and sexuality are, as the magazine describes, "fluid".
"I am literally open to every single thing that is consenting and doesn't involve an animal and everyone is of age. Everything that's legal, I'm down with. Yo, I'm down with any adult - anyone over the age of 18 who is down to love me," she shares.
"I don't relate to being boy or girl, and I don't have to have my partner relate to boy or girl."
And those aren't empty words. In May, Miley launched the Happy Hippie Foundation, an organisation to help LGBT and homeless youth.
"As long as you're not hurting anyone, your choices are your choices," she says.
Raechal Leone Shewfelt writes for Yahoo Celebrity