The song, called Blue's Freestyle/We Family, is one of three bonus tracks released with the physical edition of JAY-Z's platinum-selling album.
Other bonus tracks on the CD of 4:44, out today, are called Adnis and ManyFacedGod (featuring James Blake).
But it was the 45-second clip of five-year-old Blue's rapping that sent Twitter fans crazy.
Not all of Blue's lyrics are that clear - but that didn't matter to most fans.