Earlier this year, the former NFL quarterback sold the incredible 6,580-square-foot mansion he custom-built back in 2015 ... but nobody seemed to know the identity of the buyer, until now.

Enter Bill Maris ... a super successful tech investor who famously founded Google Ventures back in 2009.

Maris now runs his own venture fund in San Diego -- and was clearly looking for a badass place to settle down.

So, when he saw the unreal modern pad that Palmer built ... he pounced (according to Variety) -- and once you look at the pics, it's pretty obvious why he had to have it.

The modern-styled crib is wild -- it's got incredible views of the ocean, outdoor kitchen, infinity pool, spa, rooftop deck ... and even a bocce ball court!!

And, hopefully, Maris likes whips, 'cause the place has a 10-car garage!!

The whole mansion -- listed by Rande Turner of Ranch and Coast Real Estate -- is decked out in the latest tech ... with all the lights, sound and security systems controlled with a hand-held device.

Palmer famously moved to Idaho after he retired from the NFL in 2017 -- turning down TV and coaching opportunities to live the quiet life with his family.

Don't worry about Carson's bank account -- the 40-year-old reportedly made more than $174 million in contract money during his 15-year NFL career.