Before Merle Haggard died on April 6, 2016, his 79th birthday, the singer performed one of his final shows at the Mandalay Bay Ballroom in Las Vegas, Nev., on Feb. 6, 2016. The performance was talked about often following Haggard's death because, that night, Haggard's good friend Toby Keith voluntarily stepped in to help the icon out during his set. At a recent media event in Nashville, Keith recalled that memorable moment.

"He’s on an oxygen tube, sitting in the back of the bus," Keith remembers of Haggard that night. "I said, ‘What in the hell are you doing?’ He said, ‘This show paid me $100,000, and if I can get through it, it’ll pay my band until I get well.'"

Keith says that "the Hag" -- who admitted his soundcheck was "a wreck" -- then asked Keith if he wanted to join him onstage to sing a song. Keith told Haggard, "You call me up when you need me. I’ll be backstage."

"He gets onstage, and he starts off, and he sounded rough," Keith recalls. "Then, about the third song, he starts plowing, and I get a big tear in my eye; I get goosebumps. He’s killing it. He gets to about four [songs], he hits his stride."

However, Keith remembers, he soon realized that Haggard was starting to struggle: "He was playing a lot of solos." That's when Keith stepped in.

"He was only seven songs in, and I heard him say, ‘There’s another dude here from Oklahoma I want to get up.’ He brought me up. He said, ‘What do you want to do?’ I said, ‘It doesn’t matter. Whatever’s next’ … So I took off on "Ramblin’ Fever," and he played," Keith shares. "Then he goes, ‘Pick another one.’ I said, ‘What’s next?’ So, about the third one [in], he said, ‘Pick one that ain’t on the list.’ I said, ‘All right. Give me a G boys,’ and they rang it. I did "Sing Me Back Home."

"The band killed it," Keith continues. "Then he stepped up and did the sweetest, [most] bad-a-- guitar solo that you’ve ever heard. It was pure and good. He’s got that oxygen hose on, and he’s got his second wind, and that sucker’s killing it. And then we did "Okie From Muskogee," and he tipped his hat and went and got his check, and that’s the last time I saw him."

One year after Haggard's death, Keith says he's still mourning the loss of the iconic artist.

"First day I met him, I wanted him to be a great guy," Keith says. "He was a sweet man: He pulled me up on the bus, he got a guitar out, and we played on the bus for about an hour and a half. It was that way just about every time I saw him; he always took the time to sit down, talk, drink a little whiskey and get the guitar out and play something.

"It was great to me that my icon became my mentor, too -- a great icon that I worshiped," Keith adds.

Keith misses Haggard's music, of course, but it's their friendship that he misses the most.

"Merle’s the kind of guy who would call you up and go, ‘You wanna go fishing?’ I’d go, ‘Yeah. Let me know, and we’ll go fishing,'" Keith explains. "And then, three months later, you’d see him, and he’d go, ‘Where the hell were you? We went fishing, and you didn’t go.’ I’d say, ‘You didn’t set something up. You didn’t tell me when we were going fishing.’"

On April 6, 2017 -- the one-year anniversary of Haggard's death, and what would have been his 80th birthday -- Keith will be part of an all-star tribute to Haggard, Sing Me Back Home: The Music of Merle Haggard, at Nashville's Bridgestone Arena. Other artists performing include Willie Nelson, Miranda Lambert, Kenny Chesney, John Mellencamp, Dierks Bentley, Loretta Lynn, Hank Williams Jr., Ronnie Dunn, Warren Haynes, Jamey Johnson, Kacey Musgraves, Lynyrd Skynyrd and many more.

10 Essential Merle Haggard Lyrics

How Well Do You REALLY Know Toby Keith?

More From TheBoot