The No One hitmaker has written a tribute piece to the music veteran for People magazine to recognise King's achievements as she prepares to be honoured as the 2014 MusiCares Person of the Year later this month (Jan14), and she admits the 1967 track, which was made famous by Aretha Franklin, is a constant source of inspiration for her.
In the article, Keys writes, "When I think of Carole King, I think of one of the most significant inspirations of my life. She is pure, powerful and one of the greatest songwriters of all time!
"I swear when I sit down at the piano to sing and play Natural Woman, I can only daydream about the moment in her life that ignited what I would call a perfect song. It gives me chills!
"I recall vividly what it felt like the first time I heard the dimension and layers of her masterwork (album) Tapestry. I felt the same open and deeper understanding of music as when I first discovered Stevie Wonder's Inner Visions, and both are moments I will never forget.
"She reminds us that a woman alone at a piano can be as powerful as a 30-piece orchestra or an electrifying rock band. Her legacy is enduring, and her albums will be passed down to generations almost as a rite of passage."
And Keys admits she is still pinching herself after befriending the songwriting legend and performing with her at her Keep A Child Alive Black Ball in their native New York in November (13).
She adds, "I am so grateful for all the inspiration she's given me. I'll never be able to thank her enough. And when I think about the fact that I can call her a friend, I almost faint!"