Bumbles the Bee

To avoid having to go to the NPC's page, Ancel is standing on the porch of the house next to the Flightmaster at Mildenhall Meadery (/way 68.88 65.16).
However, he can also be found in a basement slightly southeast of the Flighmaster, entrance at /way 70.75 69.16. This is where you hand in the quest you get after handing him the letter and getting the secret ingredient.

If you want to get Let's Bee Friends including [npc=143730] read this first to prevent severe headaches and wasted life hours!

1. 
   
2. Make sure you are Alliance, since this Achievement is Alliance only!
3. 
   
4. Make sure you completed the Mildenhall quest chain, starting with Mayhem at Mildenhall Meadery which is available from [npc=131793] at 68.8, 65.2 after the Stormsong Valley entry quest. Check with /script print(IsQuestFlaggedCompleted(50553)) which gives back "true" if you completed the necessary quest chain.
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6. In Stormsong Valley grind [npc=141901] to obtain [item=163699]. You can find [npc=141901] on the hill right above Dead Wash east to Fort Daelin between 44.6, 42.4 and Warfang Hold (45.6, 29.4) or at the south-west coast around 24.6, 70.8. Do not grind [npc=131663] or [npc=133429], since the chance to drop it is very low!
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8. Find [npc=143128] in Boralus. She hast several spawn points. You can /target Rosaline
9. 
   
   or try to find her in one of these shops:
   
   52.7 47.9 - Scribes & Nobles (stairs to shop entrance 51.5 48.0)
   55.5 62.9 - Goldman's Cafe, Upton Borough (shop entrance 55.5 62.5)
   58.1 66.3 - Inaccessible building
   72.4 73.3 - Upper floor of an unnamed shop in southern Mariner's Row (ground floor entrance 72.6 73.7; top floor entrance for flying mount users 72.9 73.3)
   
   give Rosalind the [item=163699] and take the letter she gives you in return back to [npc=131793] at 68.8, 65.2 .
   
10. [npc=131793] gives you Bumbles the Bee, which leads to unlocking the daily quest Let's Bee Friends. Complete this daily 7 times to get Let's Bee Friends and [npc=143730].
    
    
11. 
    

As a reminder, the cave laboratory where the ingredient is located is uphill at 73:72ish - Rosaline's Apiary, not the Meadery proper, and almost due SE of the flight point.