Blake Shelton knows the fourth cut is the deepest – that’s why he’s got Lance Armstrong’s ex Sheryl Crow on his side.

Just announced… Sheryl, who’s dabbled a bit in country music, will be the Team Blake mentor when the fourth season of The Voice premieres in March.

“Sheryl Crow is one of the coolest people in the music industry,” Blake says, “and to have her as an adviser on my team is pretty darn cool.”

Adds Sheryl, “I’ve been friends with Blake for a few years now and am honored he invited me to be an adviser on The Voice this season.”

Sheryl has ties with Blake’s wife Miranda Lambert, who joined Sheryl and the legendary Loretta Lynn on the 2010 remake of Loretta’s classic “Coal Miner’s Daughter.”

In the past, Blake’s mentors have been Miranda, Kelly Clarkson and Michael Buble. The Voice premieres March 25^th on NBC.

For more on the controvery Sheryl’s ex Lance Armstrong’s gotten himself in after admitting to taking performance enhancing drugs, keep reading…

Sheryl Crow has spoken out about ex Lance Armstrong’s doping controversy.

The singer tells Entertainment Tonight “honesty is always the best bet and that the truth will set you free.”

While it’s still unclear whether Sheryl knew about the performance enhancing drugs at the time, she reveals to ET she saw “bits and pieces” of the famed cyclist’s tell-all interview with Oprah.

“To carry around a weight like that would be devastating in the long run,” she says.

Sheryl and Lance split in 2006 at the height of Lance’s career.