RS made the announcement Tuesday, taking to social media by saying he's "truly humbled to be stepping into the footsteps of the legendary Pat Sajak" -- adding he's been watching the popular game show for a very long time.

This is the grand prize for hosting game shows. 'Wheel' is one of the most -- if not the most -- successful game show ever. When you add up the viewership, it averages around 20 million a week ... making it the biggest show in TV syndication.

'Wheel' spans generations. It kicks off Season 41 in September ... truly incredible.

Ryan gives major thanks to Pat, adding "I look forward to learning everything I can from you during this transition." Ryan even calls it a full-circle moment ... pointing out one of his first gigs was on the game show "Click," another Merv Griffin venture.

Ryan says he's looking forward to working with "the great Vanna White." She has one year left on her contract and is negotiating a new one.