It was rumoured a while ago. Ziyi’s characters in Godzilla: King of the Monsters, the “Mothra Twins”, were supposed to reunite in a post-credit scene that was never filmed. Director Michael Dougherty posted the concept art of the scene on his Instagram.
The artwork shows the character of Doctor Ilene Chen, played by Zhang Ziyi, walking through a ramen bar towards a secret tunnel. There she meets with her twin sister Doctor Ling Chen, and they have a brief conversation. Then Ilene Chen enters a room containing the egg of the noble kaiju Mothra, being taken care of by her twin daughters.
The full importance of this scene will be readily apparent to those versed in early Godzilla movies lore. Traditionally, Mothra was depicted as a deity and protector of a group of humans living on an island. Mothra interacted with the islanders through the Shobijin, which refers to twin sisters who have the ability to commune with Mothra.
While the lore of the Shobjin was not explored in King of the Monsters, the post-credit scene would have confirmed they were indeed a part of the movie. It would have also confirmed that the responsibility of taking care of the Mothra egg has been passed on from Doctor Chen and her twin sister to her twin daughters, who are the new Shobjin.
Instead, the special relationship between the two Chen sisters and Mothra was only hinted at in the film. However, with the reveal of the scrapped post-credits scene, Dougherty has pretty much confirmed that a reborn Mothra will be making an appearance in the next film in the series.
To read more about it, check the article on MovieWeb.