Will was just so much fresher than Carlton that he had him replaced as Prince. Carlton used to be the prince, then he fell out of favor. All he had to do is take care of the "Aunt Viv" problem for Uncle Phil. You can see the foreshadowing in this "happy" family photo: https://s3.r29static.com//bin/entry/aa2/720x864,85/1768850/image.jpg