You can start this quest after completing The Twice-Born Warlord, by exploring Armag’s Tomb. In fact, it’ll start automatically the next time you visit your throne room after completing the aforementioned quest. Your progress in the quest Betrayer’s Flight is unimportant for this quest’s progression.
Enter your throne room and perhaps after dealing with some trivial dialogue from your companions your political benefactor(s) will arrive. Depending on your choices thus far, Jamandi and/or Natala will show up along with their chosen envoy (either Kassil or Shandra), whom they’ll foist upon you again. Make a moral choice regarding the crown that’ll soon be decorating your royal brow, after which Jamandi/Shandra will get around to business.
It’s time to formalize your political relationship, which boils down to three options, not all of which may be available given past choices. Pick "I wish to unite our powers - and make our enemies tremble at the very mention of our names. I expect you to allow my people to join the Aldori Academy, and I hope we’ll halt the patrols along our common border. - We have nothing to fear from each other." or "I desire our influence to grow as the days progress. I suggest we establish a common trade office, which will deal with issues of prosperity, for both our countries. I’d also propose we soften the customs supervision on our common border - this will help goods move faster, and will benefit trade." to ally yourself closely with the Aldoris or Surtovas, respectively, say "I promised to act as a mediating power between the Surtovas and Aldori, and I shall keep my word. I have many ideas on how we can strengthen our alliance: from the new trade agreements to creating common rules for border crossing." to enforce your neutrality, and finally respond with "Our alliance is just a formality, fixed on a piece of paper. Let’s not bother each other, and mind our own business." to distance yourself from your powerful northern neighbors. Remember, alliances come with aid… and obligations.
Make this momentous decision, then deal with any other throne room events that may be outstanding. They’re not tied to this quest, of course, but they’ll interrupt the proceedings if they pop up. Once that’s done, head outside and give a speech to your subjects, which mostly just involves making a variety of moral choices to further flesh out the nature of your regime. In addition to the title, you’ll gain a Crown - a bit of attire any good king or queen will possess. More than being a decorative symbol, however, this bit of headgear will boost the wearer’s Intelligence, Wisdom and Charisma by +6 and give a +2 bonus to Saving Throws against compulsion effects.
With that, Chapter 4 will end and you’ll move on to Chapter 5. There’s not much of a transition this time, as you’ll be right where you left off after your speech. This also won’t end the quest Betrayer’s Flight, so if you need to attend to that bit of business, you still have time. As usual, use any downtime between main quests to complete sidequests, companion quests and explore, if you wish. You have plenty of new territory in Glenebon to adventure in, after all. Over this lull between main quests you may encounter the quests Bury the Past, Turncoats, Judgment of the Gods and Deal with the Devil and the ever-recurring An Ancient Curse, in this case Part Four and Part Five.
You’ll probably have weeks - if not months - of downtime to develop your kingdom and adventure, so make the most of it. After a while you’ll get a letter from Irovetti, King of Pitax, who has invited you to the Rushlight tournament. Whatever it is, Linzi sure seems excited by it, and she promises that all Pitaxian high society will be there. Question Linzi about the nature of the tournament, Pitax and Irovetti and a variety of other topics. This starts the superquest War of the River Kings which encompasses the next main quest, The Rushlight Tournament. This also starts the companion quest A Bard’s Calling, provided you completed Turncoats earlier.