"It's one of your classic cheatin' songs," the country star tells PEOPLE.com of her new single, "White Liar," which she wrote with pal Natalie Hemby. "But we thought it would be a cool twist to say, 'I've been lying too.' "
The tune, which Lambert describes as "one of the most country songs I've written in a while – old-school and blue-grassy," is off her third CD, Revolution, which will be released Sept. 29. It's an album that also reveals a softer side to the "Gunpowder and Lead" singer.
Lambert, who is nominated for a Country Music Award for female vocalist, co-wrote three songs on the album with Shelton and admits that her happiness with him was infectious.
"I'm happy and have a really great relationship so I just figured why not talk about it?" she says. "Blake definitely had a lot of influence on this album."
But don't expect a permanent musical pairing. "We're so different so doing a whole album together wouldn't be good for our relationship," she says. "We'd end up killing each other."
Besides, she adds, a girl can only sing so many love songs. "I've got to stick with what I know too, which is revenge!"
Courtesy of Sony Music