It's the end of an era for 'The Talk.'
It was an emotional day for Sharon Osbourne on The Talk on Wednesday, when she marked the end of an era with her longtime co-worker and friend, Sara Gilbert.
ET exclusively spoke with 66-year-old Osbourne on Wednesday during Gilbert's last day of filming for the popular daytime talk show -- which airs Friday, Aug. 2 on CBS -- and she opened up about her bittersweet feelings. Gilbert announced she was leaving The Talk in April, explaining that she wanted to focus on other projects and to spend time with her three children. Gilbert and Osbourne were the only remaining original hosts of The Talk, which premiered in 2010.
"[I'm feeling] really sad but yet I'm happy for Sara, what she's going on to do, so it's like, I'm sad for myself not having that thing of coming in every day and working with Sara," a clearly emotional Osbourne tells ET. " ... We're just very close. She's probably one of my bestest friends that I've ever had because I've known her a long time but only worked with her and got close with her over the last nine years, but as I said, we live right near each other so she can't get away from me."
Osbourne broke down in tears on-air when 44-year-old Gilbert announced that she was leaving the show after nine years, and says she shed more tears during a dinner that The Conners star threw at her home on Tuesday night with their fellow hosts, which include Sheryl Underwood, Carrie Ann Inaba and Eve.
"We've been kind of, like, not talking about it but last night Sara threw us all a dinner at her house and we all cried and laughed at that dinner and we were saying when we left, 'Oh god, tomorrow's going to be awful,'" she shares. "But actually it's a celebration of what she's done here on the show and what she's going on to do."
"We're all so sad because Sara is somebody that, you know, you can't replace people," she continues.
Osbourne called it "strange" to be the only original host left going into The Talk's 10th season, noting that Gilbert always thought Osbourne would be the first to leave during the earlier days of the show. As for what she will miss most about Gilbert -- who created the show and also serves as an executive producer -- she says it's her sense of humor.
"Her fabulous dry wit, she is so quick and the thing is about Sara because she's so low key, people don't expect her to come with her one-liners the way she does and she is just the funniest," Osbourne explains. "So funny, but low-key, she's not one of these comics that's in your face."
Later, she shared one final heartfelt message for her close friend.
"Sara Gilbert, you're the best -- irreplaceable, the best, a comedy genius, the best friend I've got in my life. You've been a good friend to everybody here, we all adore you, and you know what, you're going on to great things in your life, so, I'll always be a part of your life, Ms., you're not getting rid of me."
During Wednesday's taping, both Osbourne and Gilbert broke down in tears as they shared heartfelt words for one another in front of their co-hosts and the show's audience. Osbourne also said Gilbert wasn't opposed to guest-hosting from time to time.
"Coming every day, seeing Sara -- she can read me, I can read her," Osbourne says. "If there's anything on my mind, I tell Sara. Now, it's like, I won't have Sara here. While my husband [Ozzy Osbourne] has been sick, Sara's just gone out of her way to find little things that she knows he'll like and buy for him and he considers her a friend too. She's like a sister that I never had. I can tell her things and she gives me good advice… It is like not having a sister with you anymore and it's going to be hard, but she only lives down the road. Just literally across the street. I will be paying her many visits. She's not going out from any of our lives."
Gilbert shared her own personal message for Osbourne that had Underwood, Inaba and Eve all in tears.
"I really wanted Sharon to be on this panel and I fought for her to be here, and she wanted to do it and I was so grateful," she noted, referencing the early days of The Talk. "And, I know this is, like, completely unprofessional, but right after she got the job, I called her and I was like, 'I don't know what I'm doing. How do I do this?' And she said, 'Just be yourself.' And you gave me permission to do that over these years. And, we've shared so much together, so much joy and pain. We've been there with each other and for each other through so many moments… I love you and I know this is not a goodbye and that we're going to be in each other's lives. I'll make sure of that."
In May, CBS announced that 59-year-old Marie Osmond will be joining The Talk, starting in September.
"I have so much gratitude in my heart today," Osmond said during her appearance on the show to announce the big news. "I am honored to be here. I am so excited to be here."
"I always wanted sisters," she also quipped, referring to her eight brothers.
Watch the video below to see ET's interview with Osmond, in which the busy star explains why she chose to join The Talk.