Pegi Young, who with fellow musician and then-husband Neil Young helped found the Bridge School for children with speech and physical impairments, died of cancer earlier this week. She was 66.
Pegi was married to Neil for 36 years until their separation and divorce in 2014.
She was the inspiration for some of Neil's love songs, including Such a Woman, Unknown Legend and Once an Angel.
She began as his background singer in the 1990s, sharing the stage with him at the 1994 Academy Awards and numerous tours over the course of two decades.
Pegi released three solo albums since 2007 and toured extensively on her own, occasionally with Neil on guitar.
Elton posted a photo of himself with Pegi on Instagram and wrote:
''So sad to hear of the passing of Pegi Young. A wonderful, courageous woman. A lovely artist. And an amazing mother and a crusader. The world needs more people like her.''