Star Wars: The Clone Wars debuted back in 2008. The animated series takes place between the events of Star Wars: Episode II — Attack of the Clones and Star Wars: Episode III — Revenge of the Sith. That is, until the most recent episode. Star Wars: The Clone Wars — The Final Season Episode 9 "Old Friends Not Forgotten" kicks off the Siege of Mandalore arc.
It's a highly anticipated story that, due to the show's obsolete cancellation, almost never saw the light of day. SPOILERS for the most recent episode of Star Wars: The Clone Wars, by the way.
Episode 9 follows up the prior instalment (Episode 8 "Together Again"). Unlike every other episode in the animated series, "Old Friends Not Forgotten" doesn't strictly take place between the events of the aforementioned saga episodes but rather congruently with Star Wars: Episode III — Revenge of the Sith.
The episode begins with a quick look at the whereabouts of multiple characters such as Aayla Secura, Plo Koon, and General Grievous — the latter of those noticeably appears to be more in line with how he looks in Revenge of the Sith. All of those characters are situated in the same place that they are during the events Revenge of the Sith.
During the episode, Obi-Wan and Anakin are called out to rescue Chancellor Palpatine from the clutches of General Grievous. This particular scenario is the exact one that we see play out at the beginning of Star Wars: Episode III — Revenge of the Sith. While Ahsoka and Bo-Katan are launching an offensive on Mandalore, that's what Anakin and Obi-Wan are up to.
The remaining episodes in the season will also take place during and after the events of Star Wars: Episode III — Revenge of the Sith — based on their titles and synopses.
Star Wars: The Clone Wars — The Final Season is now streaming on Disney+