Exclusive

Allen Iverson is officially mansionless -- TMZ has learned the former NBA star's Atlanta home has been sold off in a foreclosure auction.

TMZ broke the story ... Iverson allegedly defaulted on a $1.2 million mortgage which sent the $4.5 million home into foreclosure. He briefly fought off an auction ... but ultimately, he couldn't stop it.

Sources close to the sale tell TMZ ... Iverson's bank purchased the mansion yesterday for $2.5 million.

It's been a rough week for Iverson -- on top of losing his mansion, the judge in Iverson's divorce case basically just called him the worst dad in the universe.