Bel-Air season 4 will introduce the last missing Banks family member after a major reveal in the season 3 finale. Bel-Air season 3s ending featured multiple cliffhangers, one of which will lead to the completion of the Banks family as shown in The Fresh Prince of Bel-Air. Bel-Air is a re-imagining of Fresh Prince rather than a direct reboot, which means many changes have been made, particularly in the shows tone. Still, both versions of the show focus on the Banks family and Will Smith, Aunt Vivs nephew.

https://screenrant.com/bel-air-season-4-nicky-banks-introduction-tease/