This quote was said by Il'gynoth at the Emerald Nightmare raid, added in patch 7.0.3:
The boy-king serves at the master's table. Three lies will he offer you.
This quote was written in Ogmot's Dream Journal, added in patch 7.3.5:
"Three lies. Da first one been told."
So, the timeline for the first lie is between 7.0.3 and 7.3.5.
One could say that the future tense of Il'gynoth and the past tense of Ogmot's Dream Journal implies that the lie must have been told between 7.1.0 and 7.3.0, because if we stick to patch 7.0.3 and 7.3.5, then we can't say for sure what came first - the lie or their quotes.
Personally, i think the lie that has been told by Anduin, during this timeline, has been this one:
in it, he says: "My Fathe...[Pause] *conflicted look on his face*...King Varian Wrynn". Which indicates he might be either lying or grieving. In the novel War Crimes, Garrosh compares Anduin to Arthas Menethil. His appearance does resemble the prince. And with Chronicle volume 3 portraying Arthas and Jaina having a relationship, it might be revealed that he's their son.
The fact that he paused after saying "My Father", and then chose to call him by his name, may suggest that he has changed his mind during the sentence, feeling that he has slipped something that he shouldn't have said.
Since the video was posted on January 18th, 2018, that would put it in the timeline of patch 7.3.5, which was added on January 16th, 2018.
Another lie would be this one, from The Traitor King pamphlet:
"You have heard stories that the so-called 'Forsaken' were killed by the Banshee. FALSE. There was no massacre. But Anduin wants you to believe there was."
As the meeting took place in the novel Before the Storm, which takes place between the events of Shadows of Argus (patch 7.3.0) and before the Burning of Teldrassil (patch 8.0.1), this fits the timeline of the first lie.
But, that's an obvious Scarlet Crusade Propaganda. They also claim that Anduin conspired with Sylvanas to forge a pact between humans and undead, that the meeting was a staged event, and that Sylvanas is Anduin's lover and that she killed Calia and raised her as an undead on his behalf. They believe he wants to marry Calia and ensure his claim to Lordaeron's throne.
The reason i put it here, even though it's an obvious demagogy, is because of another quote being quite obvious:
At the hour of her third death, she will usher in our coming.
This quote was also said by Il'gynoth, at the Emerald Nightmare raid, in patch 7.0.3.
When she visits the Valley of Heroes, along with Turalyon, Alleria Windrunner says:
"Sometimes I feel that I have already died twice. Once when we were presumed lost on Draenor, and again when gripped by the shadow of the fallen naaru."
This quote is way too specific, random and not vague. So, it means that when Blizzard puts texts in the game, they probably mean something, and are not just random-ass blabber.
Now, we recently learned that the Void seeks every possible path and sees them all as truth. Which would mean that Anduin's lies are a possibility that might or might not have come to pass.
Plus, the recent addition of the text book "Enemy Infiltration - Preface" tells us that:
"The void lords all but welcome us with open arms. They are so preoccupied with their thousand truths that they ignore the lies we sow in their very midst."
Which, would mean that the prophecies told by the Void's servants, such as Il'gynoth and N'zoth, could be nothing but lies, sowed by the Nathrezim in the Void's midst.
What do you guys think? are Anduin's lies simply a possibility seen by the Void, a lie that was spread among them by the Nathrezim, or an actual truth that would come to pass?
Personally, i think that Anduin's lies being not true is kinda boring. It kills the enthusiasm of speculating.
But, if it's actually true, then what do you guys think the first lie could have been? I remind you that it must have been told in-between patch 7.0.3 and 7.3.5.