Osbourne became embroiled in a controversy after defending Piers Morgan in a heated exchange with Underwood, as they debated whether comments Morgan made about Meghan Markle in the wake of her bombshell Oprah interview were racist.
At the time, Underwood asked Osbourne, "What would you say to people who may feel that while you're standing by your friend, it appears you gave validation or safe haven to something that he has uttered that is racist? Even if you don't agree."
Though Underwood prefaced the question with the assertion that Osbourne has never been racist, the Brit said she nonetheless felt "like I'm about to be put in the electric chair."
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The 68-year-old added, "How could I be racist about anybody or anything in my life?"
The following Friday, Osbourne apologized in a statement posted on social media.
"To anyone of color that I offended and/or to anyone that feels confused or let down by what I said, I am truly sorry," she wrote.
She added that she felt "blindsided" by the questions from her co-hosts and reacted poorly in response, but will "continue to learn, listen and do better."
On March 26, CBS released a statement about the incident.
"The events of the March 10 broadcast were upsetting to everyone involved, including the audience watching at home," it said. "As part of our review, we concluded that Sharon's behavior toward her co-hosts during the March 10 episode did not align with our values for a respectful workplace."
Underwood, 57, is now opening up about her "traumatic" experience with Osbourne, in a three-part series on Sheryl Underwood Radio, titled "Sharon Walks Away," which she released from April 2 to 4.
Filmed about one week after Osbourne left the show, Underwood looked back through her phone to confirm Osbourne had not reached out to her since the incident.
"No, OK, I've been looking through my phone," she said. "No. I can go back as far as I can go. No."
Osbourne responded to Underwood's claims via The Daily Mail on Tuesday, saying that she had reached out to her former co-host. The outlet published screenshots of text messages from the former "America's Got Talent" judge, which have not been independently verified by E! News.
"I not only sent these messages to Sheryl but I apologized to her in person in her dressing room," Osbourne told The Daily Mail. "Why are you saying I never apologized Sheryl? What are you trying to do to me?... Why are you trying to destroy my reputation? Just be honest. Tell me."
E! News has reached out to her rep for comment.
Underwood also claimed she hasn't heard from any of her other castmates in the aftermath of the episode. The show is on hiatus until April 12.
"No, not personally," she said, noting that she has been surprised by how many people have reached out with similar experiences.
"I was startled by those people and their stories of telling me, 'This happened to me,'" she said. "I'm going to ask the people, 'Can I name names?'"
On the podcast, Underwood was asked how she felt about Osbourne's public apology, which she shared on social media on March 11.
Underwood said she had an "odd" feeling about it.
"The issue is, for me, it's about trust," she said. "I don't want to add to the chatter in a negative way that we're not coming with positive solutions and trust and growth and evolution."
For her part, Underwood said she apologized to Osbourne in person both on-air and after the show.
The "Bold and the Beautiful" star continued, "The first thing I thought was, 'Whatever role I played, intentionally or unintentionally, I am going to ask you to forgive me and accept my apology for this misunderstanding.' And I was still not getting back what you would look for, and that was disappointing."
She feels that Osbourne did not get "the best advice and counsel" on how to handle the situation. Underwood believes "if this had played out differently" Osbourne would not have left "The Talk."
After learning of Osbourne's departure, Underwood knew her former colleague had to do what was "best" for herself and her family, though she realizes haters call her a "sucker" for wishing her well.
In retrospect, she regrets that the situation happened at all.
"This was going to happen out of my control," she said.
In describing her relationship with Osbourne, she called her a "fast friend" prior to the controversy.
"You're talking about 10 years sitting next to someone. I would get advice from her. She'd been in the business a long time. And remember when I said, 'I do not know you to be a racist. I know you doing the work and being on the journey.'"
"I still love the Osbournes, from what I've known of them," Underwood later revealed. "I don't know anything other than what I've experienced with them, and this thing that has happened is disappointing to me. And maybe people don't want to hear me say, 'I still love the Osbournes.'
"I'm not saying I liked being treated the way I was treated," she said. "I'm very disappointed. And I'm trying to navigate my feelings about that, 'cause it was a trauma. Remember, I said I'm PTSD, in shock, in slow-motion."
However, she seemed to approve of how "The Talk" team addressed the controversy.
"I was pleasantly surprised at how this was handled. And that this was solution-driven. And that this was healing-driving," she said. "I was pleasantly surprised to get down to the bottom of things, so that we could correct things."
On March 12, CBS announced an internal review of "The Talk." In a statement to E! News, the network said at the time, "We are committed to a diverse, inclusive and respectful workplace. All matters related to the Wednesday episode of 'The Talk' are currently under internal review."
Underwood said the positive response from the network helped her return to work just one day later.
In her podcast series, Underwood gave further insight into the atmosphere on set after the March 10 incident.
"While there was a little bit of apprehension, I was still telling myself, 'Sheryl, this is not as hurtful as you thought. It still hurts but it seems like they're trying to get down to the bottom of something.' It didn't seem to be as odd as I felt."
"The Talk" returns April 12.