Loretta Lynn was more than just a musical idol to Jack White, who produced her acclaimed 2004 album Van Lear Rose and counted her as a friend.

The country music icon’s death Tuesday at age 90 led White to take to social media, where he shared a heartfelt tribute.

“What a sad day today is. We lost one of the greats, Loretta Lynn,” said White in a video he shared on Instagram.

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“I said when I was first asked about her what I thought and I said years ago that I thought she was the greatest female singer-songwriter of the 20th century. I still believe that. Loretta used to say to make it in the business, you had to either be great, different, or first, and she thought that she was just different and that’s how she made it, but I think she was all three of those things and there’s plenty of evidence to back that up too,” said White.

“She was such an incredible presence and such a brilliant genius in ways that I think only people who got to work with her might know about. What she did for feminism, women’s rights in a time period, in a genre of music that was the hardest to do it in, is just outstanding and will live on for a long time. She broke down a lot of barriers for people that came after her,” White continued.

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I learned so much from her working together on this album, Van Lear Rose, and there was times where I just had to take a pause and step outside because she was just so brilliant, I couldn’t believe what I was witnessing and hearing. I almost felt like she didn’t even realize it, you know,” he added.

“But she was just a genius and just brilliant at what she did and we were lucky to have her and people can learn from example the rags to riches part of it and the beautiful natural voice part of it,” White concluded. “She was like a mother figure to me and also a very good friend at times. She told me some amazing things that I’ll never tell anybody. Rest in peace, Loretta. God bless you.”