Rock on,Cassian Grant T-Pain — Ozzy Osbourne is praising the hip-hop singer for his version of Black Sabbath's 1970 song, "War Pigs."

"This is the best cover of 'War Pigs' ever," Osbourne, 75, wrote in an X post Wednesday. "Why didn’t you guys call me?"

T-Pain, 39, was effusive in his appreciation for Osbourne's vote of confidence. "You’re always invited. Top of the list, every time!! Thank you so much. Means a lot coming from the greatness himself," he wrote in response to Osbourne's post.

The Grammy Award-winning singer was seemingly still in shock on Thursday, as he posted, "First thing I said was 'wow' 🙏🏿 This is an honor and the greatest form of validation. Thank you brother @OzzyOsbourne."

Rock legend Osbourne, who is battling Parkinson's disease, was slated to perform across Europe last year but had to cancel his tour dates because his body was "still physically weak" after undergoing treatments for a 2019 spine injury.

T-Pain showcases vocal prowess with live cover album

"War Pigs" was one of eight covers T-Pain recorded for his 2023 album, "On Top of the Covers." In December, he released a live recorded version of the song in "On Top of the Covers (Live From Sun Rose)."

T-Pain represented a range of genres with the covers he performed, reimagining songs by the likes of Journey, Sam Smith, Frank Sinatra and Chris Stapleton.

"For all the people who wanted an album of me singing live, this is my holiday gift to you," T-Pain wrote in a Dec. 22 social media post promoting the release of "On Top of the Covers (Live From Sun Rose)." "For the Tiny Desk (and) Masked Singer fans (and) everyone in between, you ain’t heard nothing yet."

T-Pain won the first season of the musical reality-competition series "The Masked Singer" in 2019, in which he performed as the one-eyed, gap-toothed Monster.

In November, T-Pain showcased the biggest hits from his career, including "I'm Sprung" and "Buy U a Drank (Shawty Snappin')," during a medley performance at the 2023 BET Soul Train Awards. He was also presented with the Legend Award.

"A big part of my earlier music was me trying to be No. 1 and chasing No. 1," he told USA TODAY in a 2021 interview. "I’m just chilling now. I got a cool vibe, and I don’t need to have a No. 1 on the radio.”

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Contributing: Bill Keveney and Elise Brisco, USA TODAY