The former couple finalized their divorce in 2022.
Clarkson performed her hit 2015 single "Piece By Piece," explaining some of her changes to the crowd on Saturday, Aug. 5 (per Us Weekly).
“This song I initially wrote just super hopeful, right? And well, sometimes hopeful turns into hopeless, so here we go, ‘Piece by Piece,'” Clarkson said before singing the anthem.
The original lyrics praised Blackstock for his role as a father and a partner after Clarkson's own childhood was filled with disappointments.
In the original song, she sings, "But piece by piece, he collected me up / Off the ground, where you abandoned things, yeah / Piece by piece, he filled the holes that you burned in me / At six years old."
But in Saturday's performance, Clarkson changed many of the "he" lyrics to "I."
And instead of singing, “He never walks away / He never asks for money / He takes care of me / He loves me,” Clarkson now sings, “I just walk away / when they ask for money / I take care of me / ’cause I love me.”
She also seemingly makes a pointed reference to Blackstock as a father, tweaking the lyrics to read, "I will never leave them like you left me / They never have to wonder their worth because unlike you, I'm gonna put them first / I never walk away. I never break their hearts / I take care of things when you leave scars / Piece by pieces I restored my faith that a heart can still beat even when it breaks."
Clarkson and Blackstock share children River, 9, and Remington, 7. Blackstock also shares older kids Savannah Blackstock and Seth Blackstock with his ex-wife, Melissa Ashworth.
This isn't the first time Clarkson has called out her ex in lyrics during her Vegas show. Last month, the Voice judge revised the lyrics while covering Gayle's "ABCDEFU," singing, "F**k you and your dad and the fact that you got half / And my broken heart, turn that s**t into art / F**k you, and your view from the valley I bought you / Everybody but your dogs, you can all f**k off!"
The former couple finalized their divorce in March 2022 after a two-year custody and property battle.