WARNING: The following contains major spoilers for Star Wars: The Rise of Skywalker, in theaters now.
In Star Wars: The Rise of Skywalker, one of the most significant cameos occurs when Rey hears the voices of all the Jedi that preceded her encouraging her to defeat Palpatine. Those voices include Luke and Anakin Skywalker, Mace Windu, Kanan Jarrus and, perhaps most notably, Ashley Eckstein's Ahsoka Tano's, one of the main characters of Dave Filoni's The Clone Wars and Rebels.
Of course, fans immediately jumped to the conclusion that for Rey to hear Ahsoka's voice, she must have died in the years between the Battle of Endor (4 ABY) and The Rise of Skywalker (approximately in 35 ABY). However, Filoni posted an illustration of Ahsoka and Gandalf the Grey on Twitter, with Gandalf saying, "People thought I was dead, too. Look how that turned out..." This is a reference to Gandalf's duel with Balrog in The Lord of the Rings: The Fellowship of the Ring when he fell into the abyss to defend the Fellowship, who believed him to be dead until he returned as Gandalf the White. Similarly, Ahsoka took on a white hooded robe and wielded dual white lightsabers in Rebels.
Ahsoka was first introduced in The Clone Wars as Anakin Skywalker's padawan. Despite her good heart, tenacious disposition and brave spirit, she was framed for a bombing and expelled from the Jedi Order before she graduated to full-fledged Jedi, against Anakin's wishes. She returned in Rebels to train Ezra Briger, one of the Force-sensitive children born after Order 66.
However, Ahsoka is special in a different way: the two times she almost died, she was connected to the World Between Worlds, a metaphysical plane beyond time where the Force of the Galaxy originates. The first time, she was a teenage padawan on Mortis, a metaphysical Avalon-like planet very similar to The Rise of Skywalker's Exegol inhabited by avatars of the Force. Anakin resurrected her by channeling the Living Force of the Daughter (the light side avatar) through his body and into Ahsoka. The second time was as an adult in Rebels, when Ezra pulled her into the World Between Worlds to save her from being struck down by Darth Vader.
With Season 7 of The Clone Wars premiering in February 2020, there's a chance Filoni will fit in an explanation about how Ahsoka was able to talk to Rey through the Force without being dead, particularly if the Togruta padawan accesses the World Between Worlds once more in this final run of the series.
Directed and co-written by J.J. Abrams, Star Wars: The Rise of Skywalker stars Daisy Ridley, Adam Driver, John Boyega, Oscar Isaac, Lupita Nyong’o, Domhnall Gleeson, Kelly Marie Tran, Joonas Suotamo, Billie Lourd, Keri Russell, Anthony Daniels, Mark Hamill, Billy Dee Williams, and Carrie Fisher, with Naomi Ackie and Richard E. Grant. The film is in theaters now.