The source added, "Additionally, he's already asked for US$2m ($2.8m) for lawyer fees when he's the one driving up the cost of the divorce with seven attorneys just representing him alone."
The singer first filed for divorce from Blackstock in June, after they had been married for seven years.
In a recent episode of The Kelly Clarkson Show, she told her viewers: "My mom has been telling me since I was a kid: You are who you surround yourself with. You want to make sure you're surrounded by people that also want to be the best versions of themselves and also want a good common goal for everyone, not just themselves, right?"
"People, like, could be bad for you in a certain time. And I think that everybody just goes, 'Oh, well that means they're bad.' Well, it doesn't necessarily mean that, it just means that you're on different paths. And I think that that's okay… Everybody's on a different learning curve."
The divorce between Clarkson and Blackstock has been complicated from the very start.
Blackstock has served as Clarkson's manager and is the former stepson of country singer Reba McEntire, one of Clarkson's musical heroes. McEntire is reportedly "supportive" of the split.
The divorce came as a surprise to the world, but how did they get to this point?
A look back on their relationship shows some interesting signals as to why they eventually broke up.
The couple met in 2006 at a rehearsal for the County Music Awards, People reports.
Clarkson was on hand to perform Cyndi Lauper's Time After Time. Blackstock, meanwhile, was there to perform a duet of the country band Rascal Flatts' What Hurts the Most.
He was the group's tour manager at the time. However, the two did not begin dating yet as he was still with his ex-wife, Melissa Ashworth.
Less than a year after they started dating, Blackstock was ready to be married once again. On December 5, 2012, Clarkson took to Twitter to announce the exciting news that he had popped the question and that she had accepted.
"I'M ENGAGED!!!!! I wanted y'all to know! Happiest night of my life last night! I am so lucky and am with the greatest man ever :)" she tweeted at the time.
Clarkson originally had plans for a big, lavish wedding to take place outdoors in the US autumn. Specifically, she was eyeing an October 2013 date. However, she revealed to People at the time that she abandoned those plans after the process got too hectic with her busy schedule.
"We are so busy that we finally just came to terms the other night and were like, 'So, we change our minds and we want to elope.' We just got so overwhelmed by it – all the decisions."
She noted that between her various work obligations and acting as step-mother-to-be to Blackstock's two kids from his previous relationship, they decided that eloping was the way to go.
In October 2013, Clarkson and Blackstock got married in a small, intimate ceremony in Tennessee.
Although her marriage to Blackstock meant she would become a step-parent to his two kids, Savannah and Seth, the couple got to work quickly on adding to their family.
In 2014, less than a year after tying the knot, Clarkson welcomed her first child, River Rose, to the world.
"Our baby girl River Rose Blackstock arrived on June 12th! Thank you everyone for all of your well wishes! Brandon and I are on cloud 9! :)" she announced on Twitter.
Two years later, in 2016, she gave birth to a son, Remington Alexander.
"Our little baby boy has arrived! Remington Alexander Blackstock was born 4/12/16 & he is healthy & we couldn't be happier or more in love!" she tweeted.
The duo's marriage seemed fine at the beginning. Her career continued to roll on as she released music and got her very own talk show. However, they reportedly listed their Los Angeles home for US$10m ($14m), offering the first sign that trouble was brewing.
A little more than a month later, it was revealed that the Since You've Been Gone singer filed for divorce from Blackstock on June 4. Although little is known about the reason for the split, a source told Entertainment Tonight that the duo realised their relationship hadn't been working for a while and ultimately called it quits.
"Kelly and Brandon work together non-stop and that became a contention in their relationship," the insider said. "Brandon is the (executive producer) of her show, as well as her manager."
The source further alleged that "Kelly has always brought up wanting more children, which Brandon doesn't."
