Floyd Mayweather -- Flosses $3 Million Diamonds in Milan (PHOTO)

Here's Floyd Mayweather out in Milan ...rocking the insanely expensive diamond necklace he bought back in December -- while surrounded by his massive security team.

As we previously reported, Floyd bought the piece on a crazy end-of-the-year jewelry shopping spree -- dropping between $10 and $15 mil for the necklace and a matching diamond ring.

We're told the chain he's wearing in the pic is valued at $3 million -- and the watch is a special diamond Audemars Piguet time piece worth $1.3 million.

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