Blake Shelton's been open about the inspiration for his new album, If I'm Honest, but he recently came clean about something else: He gets nervous talking about it.

The superstar sat down with Chelsea Handler for her Netflix talk show, Chelsea, and the two chatted about Shelton's new project, his personal life and, of course, Gwen Stefani. The country star spoke candidly about his new album, revealing that the project's "timeline" began "last year, when my marriage, everything, just fell apart." He goes on to say that he was "at rock bottom and then trying to move forward" when his relationship with Stefani began to change.

"The next thing you know, this person I kind of knew -- I worked with on the show, but didn't really know her that well ... to all of a sudden find out she's going through the same exact thing at the same time," Shelton recalls, showed him that "all this has to be meant to happen."

Shelton admits his life turned around super quickly, adding, "It makes me nervous to talk about it." When Handler asks why, he waffles a bit -- but when the host asks if Shelton's the happiest he's ever been, his answer is adamant: "There's no question about that ... absolutely no question about that."

During his Chelsea interview, Shelton also says that when he brought Stefani onstage with him at Country Jam in Grand Junction, Colo., on June 18 (his 40th birthday), it was different than he expected.

"I'm doing my normal -- what I thought was -- rocking: standing with my acoustic guitar in front of the mic stand, singing my songs," he tells Handler. "And so ... I had my band work up her song "Hella Good." I thought it would be so cool to have her come and surprise [the crowd].

"It was the worst thing I could have done," Shelton continues, adding with a laugh, "All it did was make me look terrible" because the pop star had the 40,000-thick crowd jumping up and down, giving him a taste of "what it's like at real concerts."

Shelton's been busy this summer: He recently released his music video for "She's Got a Way With Words," he helped kick off NBC Sports' NASCAR coverage, and he's gearing up for a fall tour, which is set to begin on Sept. 9 in Oklahoma City.

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