The ceremony doesn't take place until 18 April, but on Thursday (08Apr21), event officials announced Allen as the New Male Artist of the Year while Barrett landed the female equivalent.
The stars were both caught unawares by the surprise news, which was broken to Allen while in a studio control booth.
"Check this out man, it came in the mail today," a colleague said as he was handed a special video card featuring a pre-recorded clip from the prizegiving co-host, Keith Urban.
After playing the message, Allen laughed and said, "Quit playin', bro!" later adding, "Oh, my God."
Meanwhile, Barrett received the news as she sat at a table and squealed in excitement as she told a member of her team, "Oh my God! Now I know why you told me to put on my makeup and get dressed!"
In recognition of their new titles, both winners have been given solo performance slots at the upcoming Academy of Country Music Awards, joining a line-up which also includes Carrie Underwood, Miranda Lambert, Kenny Chesney, Chris Stapleton, Luke Bryan, Dan + Shay, Maren Morris, Luke Combs, and Blake Shelton, among many others.
Morris and Stapleton lead the 2021 ACM Awards nominations with six apiece.
Mickey Guyton will join Urban to co-host the TV celebration, which will take place from the same three Nashville, Tennessee venues as last year (20) - the Grand Ole Opry, Ryman Auditorium, and Bluebird Cafe.