EXCLUSIVE: Gwen Stefani Opens Up About 'Shocking' Duet With Blake Shelton

But is she prepared to perform live at the Billboard Music Awards next week?

No one is more surprised than Gwen Stefani is about her duet with Blake Shelton!

ET's Katie Krause caught up with the No Doubt frontwoman at 102.7 KIIS FM's Wango Tango in Carson, California, on Saturday, where Stefani was as giddy (and surprised!) as ever about making beautiful music with her boyfriend.

EXCLUSIVE PICS: Gwen Stefani Looks Tense Meeting With Gavin Rossdale in First Sighting Together Since Split

"Anytime I've ever collaborated with anyone, it's always my favorite," she admitted. "But to do something with him -- because he's so talented and comes from such a different world -- to make music together, it was just so shocking! So amazing to do it live and share it with everybody."

Stefani, 46, is referring to last week's performance on The Voice, where she and Shelton adoringly debuted their song, "Go Ahead and Break My Heart."

The "Misery" singer and her country crooner beau will perform live once again on May 22, when they take the stage at the 2016 Billboard Music Awards. But have they been rehearsing for that big gig?

"We're not. We probably should!" Stefani laughed to ET, admitting she wasn't quite sure what the appearance would like like yet. "It was amazing doing that song live [on The Voice]. It's incredible to do."

WATCH: Gwen Stefani Gleefully Supports Blake Shelton at 'Angry Birds' Premiere

Stefani also got candid about her newest album, This Is What the Truth Feels Like, which was well-received after dropping in March.

"I prayed for that, I promise you," the mom-of-three said of the incredible reception. "I just so badly wanted to make something good out of something bad. I had to. I knew that that was my duty."

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Stefani was especially excited to perform at Wango Tango, as she finally feels good about songwriting again. "It's just so fun to have new music, especially when I have not written a good song that I love in such a long time," she told ET. "This record… it happened so fast. It's such a shock that I could get in that place. It was so what I needed to do, so now that it's done and sharing it with people, it just feels so incredible."

WATCH: Gwen Stefani Is Barefaced and Beautiful in Makeup-Free Selfie

Last year, Stefani split from her husband of 13 years, Gavin Rossdale, and the divorce was finalized last month. She began dating her fellow Voice judge, Shelton, later that fall. The 39-year-old singer went through his own divorce with ex-wife Miranda Lambert last summer.

Get the full details on what you didn't see during Stefani and Shelton's Voice duet in the video below.

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