Serena Williams & Hubby Honeymoonin' On Private Island, $35k Per Week!

Here they are ... newlyweds Serena Williams and Alexis Ohanian chillaxin' on an insanely expensive private island in the Bahamas during their honeymoon -- that they booked on Booking.com.

We're told the villa runs $35k per week -- and you can only get to it if you have an aircraft or a boat.

The photos of S & A at the villa were taken by a drone but we're told the couple willingly participated in the shoot in connection with Booking.com ... so, it wasn't a crazy rogue paparazzo invading their privacy.

Serena also posted on Instagram about the villa -- "A week in paradise. Thanks @bookingcom for helping us find the perfect honeymoon villa. #BookingYeah."

All signs point to Serena getting either paid or a huge discount for the endorsement -- despite the fact both she and her Reddit co-founder husband are LOADED!

#HowTheRichStayRich