One of Toby Keith's final concerts before his death was a special one ... with his mom Carolyn making a hilarious appearance on-stage, much to the surprise of delighted fans.

TMZ has obtained footage showing the late country icon in great spirits during a Sin City show on December 12 at the Park MGM Las Vegas ... which sadly ended up being one of his last. His last concert ended up being a couple days later at the same exact venue.

In the video, you can see him bring his mom, Carolyn, onstage -- joking around with her and encouraging her to tell audience members to "go to hell" -- which she did, no questions asked. Everyone got a big laugh out of it, and it certainly served as a sweet moment.

Carolyn was waving and rolling with the punches while sharing the spotlight with her son ... with the bond between them evidently strong. No doubt, it must've been a cherished memory for Toby ... who did, in fact, look a little frail in the clip ... but, for the most part, delivered an epic show with his signature vocals. His fans must have loved this too.

As we've reported ... Toby passed away Monday night while surrounded by his family, according to a statement posted to his Facebook page.

He'd been battling stomach cancer ... which he was diagnosed with in 2021. Toby announced the diagnosis in June 2022 ... adding at the time he was receiving chemo and radiation therapy, and had also undergone surgery.

Toby's passing has been a massive loss for the country music world ... during his 3-decade career, he released 24 studio and compilation albums and 2 Christmas records, generating $40 mil in worldwide music sales.

Last September, he also won the Country Music Icon Award at the People's Choice Country Awards 2023 -- a major feat for any country artist.

Toby was just 62.

RIP