This is a picture of Joni Mitchell that I took in the spring of 1969. I was living with her in Laurel Canyon, Los Angeles, which is where I wrote the song Our House. I later recorded it with my band Crosby, Stills, Nash & Young.

At the time, Joni and I were blazingly in love. Our relationship was heaven to me, and it was heartbreaking when it was over. She was an incredibly talented woman; I have no idea what she was doing with me.

Sometimes in California it gets gloomy when the clouds roll in off the ocean. It was one of those cloudy days when I managed to get this shot of Joni without her knowing. She was listening to her album Clouds, which she had just finished. There are a lot of places you have to go before you finally have the courage to put out a record; here, Joni was checking the acetate for clicks, pops and scratches. It's very interesting being in a house with two crazy musicians: you have to have great respect for the creative process, and I certainly didn't want to interfere when Joni was in that moment.

I got into photography when I was 10. My father bought a camera from a friend at work and took us to Belle Vue Zoo in Manchester to shoot pictures. Back at home, he would cover the window with a blanket, put a blank piece of paper into a colourless liquid, and all of a sudden this image appeared from nowhere, like magic.

Having had millions of pictures taken of me since my career started in the 1960s, with the Hollies, I know that when a camera is pointing in your direction, you immediately try to look like James Dean. I hate that; I don't want anyone to know when I'm taking their picture.

This was shot through the back of a hole in a kitchen chair. I only took one frame, as the click disturbed her. What I saw in my mind before I pressed the shutter, I knew I'd got. When it was developed it was a thrill to discover that the composition was strong, and that the density between the white and black was good, too. I think she knew it was a good picture. This was not after two hours of makeup; it was Joni after breakfast.

I think this photograph shows how dedicated Joni is as an artist. You can sense that she has gone to another place. It is a quiet moment of rock'n'roll energy.