A source said Blackstock "chose to move on with someone Kelly knew and trusted," which "just adds to the person he ended up being to her."

Kelly Clarkson canceled her appearance at the Band Together Texas Benefit following the death of her ex-husband Brandon Blackstock. She and the late music manager share daughter River and son Remington.

Now, an insider close to Clarkson is revealing to the Daily Mail how she allegedly reacted to the situation when she discovered her former assistant, Brittney Marie Jones, was in a relationship with Blackstock. The source described the fallout as “just the icing on the cake of the disappointment [Clarkson] felt over the delusion of their marriage.”