Fat Joe is reeling in emotion ... currently mourning the death of his father.

On Wednesday, Joey Crack let the world share in his grief that his father Ernesto Cartagena had passed on, posting several never-before-seen family photos.

The world knows Fat Joe as a hip hop legend ... but Joe gave his father the credit for being a true legend in his own eyes.

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In his biography, Joe admitted to being a hard-headed child, but applauded his father for showing him the true meaning of hard work.

Joe grew up to use his celebrity status to enact good -- more values instilled in him from his father.

RIP