Brett Eldredge is a huge Frank Sinatra fan. Darius Rucker is a huge Frank Sinatra fan. They may not have had a total "Are you thinking what I'm thinking?" moment, but the result was the same. During Eldredge's set at the sixth-annual Darius and Friends concert for St. Jude, the two country stars introduced a horn section before breaking into back-to-back Ol' Blue Eyes songs.

"Both are two songs I love," Eldredge told ToC of "Come Fly With Me" and "That's Life" prior to the show. "He's a huge Sinatra fan. So we already bonded on the road but when we both found out we're big Sinatra fans we're like, you know ... that's a good guy to learn from."

Unexpected covers became the expected by the time the all-star show was finished. Rucker's cover of Prince's "Purple Rain" — well-known and appreciated by this faithful Wildhorse Saloon crowd — closed the show. Other highlights included Rucker joining Steve Wariner for the Beatles "Get Back" and a Thousand Horses for the Black Crowes song "Hard to Handle." Neither were perfect, but the moment was, as everyone knew all money was going to a good place.

Totals for the 2015 Darius and Friends concert will be released later this week, after Tuesday's celebrity golf tournament. In 2014 the country singer raised over $120,000. He has netted the children's research hospital over $400K since he began in 2010. Cancer research is a cause that continues to hit home for the event's namesake. Just this week he posted a message on Twitter encouraging a family member of one of his crew members to get well soon:

"She's come out to shows," Rucker says of Megan, "and she's not doing well. We just tweeted out our love and wishes ... it's always sad."

Rucker began the show singing "Alright," before bringing Scotty McCreery out. The one-time American Idol star performed three songs, including a cover of George Strait's "Check Yes or No," before giving way to Brothers Osborne.

The sibling duo nabbed the night's first standing ovation. John Osborne's solo on their current single "Stay a Little Longer" was a two-minute-long blistering jam that transitioned right into a cover of ZZ Top's "La Grange." About six solos later they were done, and the crowed was primed for a Thousand Horses. The band didn't disappoint with "Smoke" and "Travelin' Man," two songs from their just-released Southernality album.

Rucker says it's not difficult for him to keep the show and message year to year as the lineup keeps changing. "I think just having different artists every year keeps it kind of fresh and you'll still put up with my little two hits here and there," he says.

Little Big Town also played, singing "Girl Crush" and "Pontoon" to a sold-out Nashville crowd.