Selena Gomez's New Home -- Millions Dropped On Anti-Bieber Mansion

Selena Gomez is the proud new owner of an anti-Bieber fortress, TMZ has learned.

Real estate sources tell TMZ, the deal closed last week -- Selena threw down roughly $3 million for a 5-bedroom 7,200 sq. ft. Calabasas mansion, located minutes away from the Kardashian empire in Hidden Hills (great for lunch dates with Kendall Jenner).

We're told Selena didn't have many demands while house shopping -- but she refused to budge on one thing ... the home could NOT be in The Oaks ... aka Justin Bieber's old hood.