Country star Lee Greenwood – whose hit "God Bless the U.S.A." has become America’s unofficial national anthem – is cheating on his fourth wife with an ex-girlfriend, The ENQUIRER has learned exclusively.

She’s a successful Tennessee businesswoman who is 24 years younger than the 66-year-old singer.

"The woman and Lee first dated a long time ago, but they’ve recently rekindled their relationship after she went through a divorce," a source confirmed to The ENQUIRER.

"She bumped into Lee about five months ago at an airport, and they swapped numbers. Lee’s been meeting her at hotels around Nashville as often as once a week. He’s told the woman that he has no plans to leave his wife, and she’s fine with that."

Greenwood is marriedto 42-year-old former Miss Tennessee USA Kimberly Payne, who’s now president of Greenwood Productions, Inc. They wed in 1992 and have two sons.

The ENQUIRER caught Greenwood and his mistress leaving the Hilton Garden Inn near the Nashville airport on Sept. 10.

"They came out of the back door together about 2:15 p.m.," an eyewitness divulged.

"Lee was wearing a Tennessee Titans football jersey and got into his white pickup truck. His girlfriend drove off in a black Cadillac Escalade."

When contacted by The ENQUIRER, the woman admitted meeting Greenwood at the hotel, but insisted that he was simply giving her advice on her pending divorce.

Greenwood’s spokesman told The ENQUIRER that the attractive redhead is an "old friend" of the singer, but didn’t deny he’s carrying on an extramarital affair with her.

"Lee is a devoted husband and father who meets with fans, business associates and potential promotional partners often," said his spokesperson Kirt Webster.

Stories of Greenwood’s cheating heart don’t surprise those close to him.

A woman who says she dated Greenwood when he was married to a previous wife said: "We were together about 10 years, and I doubt I was the only girl he cheated with."

Meanwhile, a Greenwood family member told The ENQUIRER: "The only plus for the new girlfriend is that Lee is kind of showy, so she could get some nice gifts."

The family member also confirmed that Greenwood favors redheads.

When told that the woman is a redhead, the source said: "That’s Lee – up to his old tricks. He may be 66, but he’s still a hound dog!"