The 38-year-old attended celebrations for Caitlyn on Sunday, with his wife Kim Kardashian, 34, and their two-year-old daughter North.
According to family sources, the rapper surprised everyone by serenading Caitlyn, formerly known as Bruce, with a cover of Stevie Wonder’s Isn’t She Lovely.
HollywoodLife.com reports that an insider told them: “Out of nowhere, Kanye asked Caitlyn and the others who were there to have a seat because he wanted to say something.
"He said, ‘This is for you, Caitlyn’, and he just started belting out the most wonderful rendition.”
Caitlyn, who was also joined by her children Khloe, Kendall, Burt and Brandon, was allegedly reduced to tears by Kanye’s touching tribute.
The sourced added: “The whole point was for Kanye to convey to Caitlyn that she’s lovely and that everyone in that room, including himself, loves her. Caitlyn’s mouth dropped and she was in tears.
"She thought it was beautiful and epic.”
Caitlyn made her sensational debut as a woman last month, following her tell-all interview with Diane Sawyer for ABC.
During the chat, she revealed that Kanye helped Kim to accept her new lifestyle.
She told Diane: “He says to Kim, ‘Look, I can be married to the most beautiful woman in the world, and I am. I can have the most beautiful little daughter in the world, and I have that. But I’m nothing if I can’t be me. If I can’t be true to myself, they don’t mean anything.
“Since then, Kimberly has been, by far, the most accepting, and the easiest to talk about it.”