The 33-year-old singer -- who gained fame as the first Idol champion in 2002 -- was a guest on The Ellen DeGeneres Show, where she opened up about her heartbreaking "Piece by Piece" performance that brought judges Keith Urban, Jennifer Lopez and Harry Connick Jr. to tears.
In a sneak peek clip from the episode that airs on Thursday, Clarkson breaks down the real reason why she was so overwhelmed by emotion while belting out the song on stage.
"I came off [stage] almost in tears for a different reason because I was so embarrassed," Clarkson explains. "'I was like, 'Oh God, this is my final thing on Idol and I could not hold it together.' I was almost losing it almost the entire song."
"I was proud of myself for making it as far as I did," she continues. "My husband [Brandon Blackstock] knows me well. I came off stage and he was like, 'Don't ruin it. Don't ruin the moment.' Because I was like, 'It was so embarrassing! I cried the whole time.' I didn't realize it was going to be that bad. And we were rehearsing that day and I just couldn't get through it. My 1-year-old [River Rose] is running around the same hallway as I was [at] 19."
"The song is incredibly sad," she says. "It's sad, but hopeful, because a lot of us, we didn't have a bar to set as far as finding love and relationships. Or friendships in any form."
"So my sister [Alyssa] and I had a conversation afterwards -- I ended up writing this song about how lucky we are because we both found incredible fathers and just lovers and men and just partners," she adds. "I feel really lucky because I feel like a lot of girls with daddy issues don't end up that way; we end up going the same [direction]."
Clarkson -- who is pregnant with her and Blackstock's second child -- also opens up about her baby girl, River, whom she says has an obsession with DeGeneres because she voiced the beloved character of Dory in Finding Nemo. She says they are both really excited for the sequel, Finding Dory, mainly because they've "watched [Finding Nemo] enough."
"I feel like we live together because you're always in my house," Clarkson jokes.
Following her appearance on the show, Clarkson took to Twitter to share an adorable snap of baby River in costume, a gift from the 58-year-old host.
"River LOVES her Dory costume," she tweeted. "Thnx @TheEllenShow Can't wait 4 'Finding Dory' We 'found' Nemo a billion times already!"
Last month, the brunette beauty got candid about her relationship with Blackstock and the significant role he's played in her and River's lives. She said that watching her husband "love on his daughter all the time" is "hard to watch but beautiful" during a radio interview with Ryan Seacrest.