It is no secret that former professional boxer Floyd Mayweather loves bling. He even writes about his jewelry purchases on Instagram. That is where many learned of his most recent purchase: Jacob & Co.’s $18 million Billionaire diamond tourbillon watch.

First introduced to the world in 2015 at that year’s Baselworld, the Billionaire timepiece is a one-of-a-kind watch that Jacob Arabo created in affiliation with Flavio Briatore and his Billionaire Lifestyle SARL company......