Blake Shelton knew that Toby Keith had been facing a difficult cancer battle, but still, in Shelton’s eyes, the Big Dog loomed larger than life.

Keith’s death on Monday (Feb. 5) came as a painful shock, the younger star admits in a remembrance he shared to social media.

“Even though I knew about your battle these last few months I still never imagined this day,” Shelton writes on Twitter, sharing an identical message to his Instagram Stories. “Anyone who knew you knows what I mean.”

“You were the toughest man I ever met,” he continues. “Thank you brother for being a friend, a hero and an inspiration. There will never be another Toby Keith.”

Shelton’s close friendship with his fellow Oklahoma native stretches back two decades. Keith took a young Shelton out on tour in 2004, and they’ve been friends ever since. Last September, Shelton presented Keith with the Country Icon Award at the first-ever People’s Choice Country Awards, and also performed “Who’s Your Daddy?” at the awards show in Keith’s honor.

Keith’s death was announced via a statement posted to his social media, which said he died “peacefully” while “surrounded by his family.” The country legend is survived by Tricia Lucus, his wife of nearly four decades, as well as three children, several grandchildren and extended family. He was 62 years old.