I’ll explain you how to easily unlock it.
Hidden King/Queen Title Guide
To get the title, you need to clear a level of the first tower in less than 10 seconds.
To do so, i’d recommand be around 500-600 ilvl, you may succeed with lower ilvl on class with a strong dps awakening.
Then you go to the level 5 of the tower boss, and when the fight start you instantly use your awakening to one shot hit (or finish him if not strong enough).
Worked in 2,7 seconds for me.
Enjoy, and you’re welcome!