The two artists are among a host of top musicians invited to pay homage to the late King of Rock and Roll and his famed 1968 TV special, which was performed live, and Keith reveals he really hit it off with the rockstar hitmaker.
"He's the real deal," the singer told E!. "He's so eclectic. So steeped in all kinds of music. I love him."
Post Malone's taste in tunes wasn't the only thing Keith admired about his new pal: "I wanted his suit," Nicole Kidman's husband laughed. "It was so bad a**."
It's not known which Elvis song the pair collaborated on, but Post and Keith will feature alongside Shawn Mendes, Blake Shelton, Darius Rucker, Little Big Town, Adam Lambert, Dierks Bentley, the Pistol Annies, and John Fogerty on the upcoming show, which will be co-hosted by Elvis' only child, Lisa Marie Presley, and her actress daughter Riley Keough.
"The 50th Anniversary of the Elvis Comeback Special", which was recorded in Los Angeles over two days in October, also includes pre-taped sets performed by the likes of Jennifer Lopez, Carrie Underwood, Ed Sheeran, John Legend, Alessia Cara, and Yolanda Adams, who all chose classic Elvis cuts for the tribute.
In addition, rare clips and interviews with Elvis himself will air as part of the TV event, which is expected to be broadcast in early 2019.