I have confirmed this personally and it feels epic. This was brought up at our community forum and it is under discussion. Thanks, Entropy.
When you loot a random drop named “The Lady’s Necklace” from Deatholme Acolytes at Windrunner Spire – on the western side of Ghostlands, the item has an inscription: “There’s an inscription, which reads: To Sylvanas. Love always, Alleria.” You take the object to High Executor Mavren at Tranquillien village. He will send you to Sylvanas in Undercity.
High Executor Mavren: This is quite extraordinary! It appears to be a gift to Lady Sylvanas Windrunner from her sister, Alleria!
You must take it to her in the Undercity at once! The lady holds court in the Royal Quarter.
To get there, use the portal in Silvermoon City to cross over to the Undercity and take the elevator ride down into the city proper. Use your maps if you need help finding the Royal Quarter.
The quest objective is to take The Lady’s Necklace to Lady Sylvanas Windrunner at the Royal Quarter in Undercity. After the recent closed beta patch, the claim is that the memories of the necklace brings Sylvanas to a sadness, and she begins singing a awesome song titled: “Lament of the Highborne” – that reminds fans of the elven princess from Lord of the Rings film.
You can read the full transcript of the quests, lyrics of the song in english and thalassian and screenshots HERE
