tmz.com
Fat Joe has just turned himself in to prison to serve his 4 month sentence for tax evasion.
The rapper — real name Joseph Cartagena — is officially in custody at the Federal Detention Center in Miami.
As TMZ previously reported, Joe pled guilty back in December to stiffing Uncle Sam on a boatload of taxes for the years 2007 and 2008 … more than $1 million total.
He originally faced up to two years in the slammer for the crime — but was ultimately sentenced to just 4 months and a $15,000 fine, plus one-year supervised release.