While many were surprised that Emperor Palpatine made an audible cameo in the first trailer for Star Wars: The Rise of Skywalker, it appears Lucasfilm had planned on bringing him back since working on The Force Awakens.
In an interview with MTV News, Lucasfilm president Kathaleen Kennedy divulged this information when asked when Palpatine’s involvement in the new trilogy was first discussed, saying “That goes back to when we were talking about Force Awakens, and you know, just the whole blueprint of where we’ve ended up now has kind of been in the works since then.”
Source: IGN.com Lucasfilm Planned on Bringing Back Palpatine Since Force Awakens