Destroying Anduin revealed a previously unseen film in the game, and it's certain that the community is slightly divided on what was revealed particularly regarding the appearance of a key someone in WoTLK Gold lore. More spoilers below.

The film depicts the heroes of Azeroth struggling against Anduin. Just as the corrupted leader of the Alliance looks set to be consumed completely by the Jailer's Domination magic, the spirits of both his father Varian and his friend-from-across-the-aisle Varok Saurfang place their hands upon him. Informing Anduin that both the Shalamyne blade's legacy along with their personal legacies, are with him, Anduin is able to be free of the influence of the Jailer.

Then the soul of Arthas comes to life in the form of an orb of blue. It's been thought for a long time that Arthas would have some role as a character in Shadowlands. Arthas was a character in an early Afterlives animated short before the release of the expansion alongside his mentor Uther was a prominent role in the narrative of Shadowlands. The story has hinted in Shadowlands in that the Jailer is ultimately responsible for the corrupting of Arthas however it remains to be determined if the character would appear in any way.

When Anduin escapes the Jailer's spell He is likely to have released the fragment of Arthas soul which was trapped inside Shalamyne and transformed it into Kingsmourne. Arthas is involved in the fight in the fight against Anduin to a large way, with players at one moment facing the ghost of Remnant of the Fallen King, which appears exactly like the former Lich King and uses numerous of his legendary powers.

Characters such as Jaina and Sylvanas examine the remains of Arthas and examine his legacy with cheap WOW WoTLK Classic Gold commenting that she once had a hatred for and even hunted Arthas before he eventually become as much of an animal as he was. She then dismisses the spirit and calls for the name of Arthas Menethil to be forgotten.