Pat Sajak is NOT coming out of a short-lived retirement to host the upcoming "Celebrity Wheel of Fortune" season -- instead, this was always in the cards ... TMZ has learned.

Here's the deal ... when ABC announced Wednesday Pat would be hosting the fifth season of 'Celeb Wheel' this fall, there was speculation he was pulling a Tom Brady by quickly backing out of retirement.

That's not exactly the case, because sources with direct knowledge tell us it was always part of Pat's succession plan to do one last season of 'Celebrity Wheel' ... before riding off into the sunset and completely handing over the reigns to Ryan Seacrest.

We are told that Pat had one more year of the show's primetime edition as part of his prior contract.

Pat's already done with his 41-year stint on the OG syndicated "Wheel of Fortune" -- his last new episode aired in early June -- so that's why folks were confused when ABC announced he would be doing 'Celeb Wheel' again.

Our sources say Pat has not filmed any episodes for 'Celeb Wheel' ... it airs in October and later this summer he will be in the studio filming those shows.

Once Pat finishes this last season, we're told Ryan will take over for the following season. So, this fall will mark Pat's truly final appearance on any 'Wheel of Fortune' show. Soak it up!