Very important details about Avengers 4 are still being speculated. Mark Ruffalo gaveaway one of the most important details. Mark Ruffalo said following statements on a podcast program on November 21, 2017. At the beginning of this program, he says that the Avengers Infinity War and Avengers 4 were filmed together. Actually, there's not much interesting detail here. But he later says that he enjoyed working with Tilda Swinton (Ancient One) and Cate Blanchett (Hela). In Thor Ragnarok, he starred with Cate Blanchett, but in Doctor Strange, he had no role with Tilda Swinton, the Ancient One. He was not in the movie at all.
We will see Ancient One in Avengers 4!
After this incident, everyone was silenced, and there was no significant detail about this for a long time. In fact, many people even thought that he got mixed up, until the last day.
One of the Avengers 4 producers Michael Grillo and screenwriters Christopher Markus and Stephen McFeely, made various statements about the Avengers 4. It turned out that Tilda Swinton (Ancient One) is actually in the movie.
So we find out that Tilda Swinton, the Ancient One, will be in Avengers 4. In fact, it is believed that the Ancient One was the one who told Dr. Strange that there was an only way to win the battle against Thanos.