A source tells ET that the former couple, who tied the knot in October 2013, decided to call it quits "after realizing the relationship hasn’t been working for a while."
"Kelly and Brandon work together non-stop and that became a contention in their relationship," the source says. "Brandon is the EP of her show as well as her manager. Also, Kelly has always brought up wanting more children, which Brandon doesn't."
A second source close to Clarkson's talk show show production tells ET that many on staff were "in the dark" about her decision to file for divorce. The American Idol alum's show remains in production remotely, with interviews scheduled to take place over Zoom through June 24.
"Everyone loves Brandon. He's an integral part of the show," the source says. "Everything is run by him and he's a hands-on, decision-maker, not just Kelly's husband/manager."
According to court documents obtained by ET, Clarkson filed for divorce from Blackstock on June 4 in Los Angeles, citing irreconcilable differences. She is requesting joint legal and physical custody of their two children, River Rose, 5, and Remington Alexander, 4. Blackstock has two other children, Savannah and Seth, from his previous marriage to Melissa Ashworth.
ET spoke with Clarkson last August about how she and Blackstock made their blended family work.
"I think we do really well. We're lucky, we're a blended family, but we believe in the same kind of discipline for our children," she said at the time. "We have very similar goals in life, as far as personally what we want to accomplish. I mean, we're different, we work on that because we're two different worlds coming together, but it's working."
"The best advice to give people is you’ve really got to, and this is going to sound really weird, but it's an intimacy vibe," she added. "Like, you've got to be intimate with each other regularly. You’ve got to make time for date nights, you’ve got to have that intimacy, that one-on-one [time] often."
Hear more in the video below.