Stern began the show by gushing over Stefani and Shelton's "incredible storyline," calling the pair a "hot couple." Stefani revealed she first developed a friendship with the country crooner before her divorce from Gavin Rossdale, who allegedly cheated on her with their nanny, went public last August.
"I didn't know what I was going to do!" she explained about what life was like after splitting from the Bush frontman following nearly 13 years of marriage. "I was in a panic. I was, like, in hell. I was in my hell of my life. And I was going back to The Voice in the middle of it with this big, huge secret."
"It was just one of those things where I just -- I didn't want anyone to know what was going on with me, I didn't want to rush anything in my mind," Stefani, 46, confessed. "I wanted to try to figure everything out."
Stefani admitted that she "prayed a lot" during that tumultuous time, crediting her parents and God for helping her get through it. "I feel really grateful," she added. "When you have really bad things happen to you sometimes, I feel like that's a little bit of an awakening, and now I feel so awake, you know what I mean?"
Stern then joked that Shelton "worked his way in there" fast, but according to Stefani, that's not exactly how it went down.
"It wasn't like that at all," Stefani replied, laughing. "It was the most unlikely situation to ever happen."
"I didn't know Blake," she said, explaining that the two had barely talked before she returned to tape The Voice last July. "In the show how it works is, I'm in hair and makeup for about 400 hours, and we all have separate trailers -- we're all in a compound in the same room but in trailers. Nobody goes into each other's rooms and nobody talks to each other until we're [about to go on camera]."
The blond beauty revealed that because there wasn't really a lot of down time off-set, she only chatted with Shelton and their fellow coaches, Pharrell and Adam Levine, while they were in front of the cameras, or in between the blind auditions.
"You're doing 14-hour days, trying to shoot and stuff," she added. "So, I didn't know him, but you get to know him on the set, because he's so funny and he's so lovely, and I was actually -- from the outside, he looks so happy and all those things."
"When I came back to the show, I had this huge weight on me, and nobody but my parents, and obviously everybody involved, [knew,]" she continued. "We all sat down before we were going to go out to the blind [auditions] with the producers, and we were all on the couches and we were mic'd up and everything."
That's when she first discovered Shelton, 40, had gone through an eerily similar situation.
"Blake was like, 'I gotta talk to you guys,' and he basically made his announcement," she remembered, of him filling in the cast and crew about his divorce from Miranda Lambert. "I think I might have went white and was in shock, because it felt like he was exposing me, do you know what I'm saying?"
"And I just couldn't even get my head around it," she added. "It was during the blind [auditions], during that time, he came up to my chair. It was the first time he had ever walked to my chair, and he was like, 'I'm sick from what I'… and I never saw him look so upset."
Stefani explained that moments after that encounter, she went up to him and said, "I gotta talk to you!" She couldn't reveal too much about her own situation to him at the time, but she let him know she could relate.
"Then we just started this friendship, which was just unbelievable that God would put us in a position to have each other at that moment, in the same exact moment," she revealed. "His thing had been going on since January, mine since February."
"I wasn't trying to start a relationship," Stefani continued. "I was just trying to not die. There was no plan."
The mother of three doesn't remember calling the "Came Here to Forget" singer on the phone in the beginning of their newfound friendship, but says they "started emailing" here and there. "The Voice, people don't understand, is all pre-taped," she dished. "You only have like three days [where] you're together. And he doesn't even live in L.A."
"It was an incredible gift to be able to have a friend," the No Doubt frontwoman gushed. "It was crazy to be able to also musically know somebody in such a different genre of music. He ended up writing a song that he sent to me, and I wrote back to him on that song, so we actually got to write a song together."
That song, of course, is "Go Ahead and Break My Heart," which appears on Shelton's latest studio album, If I'm Honest. To re-live highlights from the first time the pair performed it together on The Voice stage, watch the video below.