This is it - the final boss fight and scraps against Ifrit and Behemoth King as part of Chapter 14. Good luck!
The safest strategy here is to use the Warp Points along the front of the building to stay out of trouble and get some distance to allow for maximum power Warp Strikes, use Link Strikes when available, and use Armiger when it's charged.
You'll need to manage the rest of the party's health carefully - we found Prompto to be a particular liability during the battle - but you should remain relatively safe as long as you avoid direct confrontation.
When he's down to around 50% HP you will be able to summon divine intervention and finish the battle there and then, but you can also finish him off by hand if you'd prefer - just remember that there's still two more bosses to deal with so conserving healing items is important!
When he's down you'll probably want to save and rest up again before opening the gate and moving on, but when you're ready make your way through and head towards the citadel.
This may look familiar from the opening of the game all those hours ago, so as before head towards the flames to trigger a cutscene.
The fight comes in two phases, and the first is relatively painless: get a fair amount of distance and make a Warp Strike, and repeat a few times - each hit should do quite a large amount of damage, and it should only take a few before you're able to summon divine intervention.
The second phase is tougher, but the same strategy as the Behemoth King works well - Warp Strike from as far away as possible to wear him down, use Warp Points to heal and stay out of trouble, and watch everyone else's health.
This time you'll need to wear him down to nothing before you can summon divine intervention and take him out once and for all, but with patience it's a simple enough task.
Enter the Citadel, ride up in the elevator, and enter the throne room. You're on your own again now. Climb the steps to the right of the throne and over the rubble on the other side, then use the Warp Point below to enter the fray.
Need more help? Our Final Fantasy 15 guide and walkthrough can provide tips on main story, as well as the open-world's many quests and activities. Learning how to get AP fast, EXP fast and money or Gil fast will aid you in many optional dungeons and tombs - including how to open and explore their locked doors. There's also plenty of interesting side-quests, too, such as the Scraps of Mystery and Professors Protege frog locations. And if you want to get around easier, you can rent a Chocobo, learn the infinite sprint trick and later in the game, get the flying car Regalia Type F. There's also more to see and do with DLC, such as Episode Gladiolus and Episode Prompto.
Final boss fight
The final confrontation is deceptively simple. Ardyn has similar Warp abilities to you so he can be hard to keep track of, but beyond that it's a simple fight.
Be sure to block and parry when prompted as it can leave him vulnerable to a sustained attack afterwards, but for the most part a simple cycle of using Warp Points to heal then Warp Strikes to do extra damage will quickly knock him down to 50% HP.
The second phase is reminiscent of the fight against the Leviathan - you'll both be airborne, but by locking on and holding attack and Warp Striking if he manages to pull away you can have him down to practically nothing with a minimum of fuss.
The final phase sees you back on the ground, but Ardyn is severely weakened and doesn't put up much of a fight. Hit him a few times to trigger a QTE, deal the last few blows, and watch the story come to its conclusion.
When the credits are done, it is possible to head back to the wider world of Lucis to make a start of the game's wealth of end-game content, of which there is plenty, including optional dungeons and tombs. Our Final Fantasy 15 guide and walkthrough has an overview of what else you can tackle!