Hope you enjoy.

Previously;

"It's time to pass down the crown. I have had enough, waiting for them to find their mates. They are already the age." The King said. 
"We can't push them. Give them time." The Queen said, calmly. While resting a hand on her mate and husband. 
The king had calmed down and turned to the servant and said," Go fetch the princes and tell them to come here, say it is about their mates." With a quick "yes, your majesty" the servant scurried off in search of the princes. To deliver the message. 
To another, he spoke with a glance to his Queen. Who replied with a soft smile and a curt nod. 
"Fetch the messenger, and sent out a message. It is time for the Mate Ball." The King said.

Third POV:

After having had finished all of their work.  All of the six princes were gathered in their library/meeting room.  Where they have been meeting together since they were kids.  With window's occupying part of the wall, hours spent gazing at the night sky.  Filling the long nights of memories. (photos below of the library).  Shelves filled up to the brim, with books, along with years of memories.

Kris was occupying one of the couches, with a book in his hand, reading.  Yixing or Lay, was seen being his usual sleepy self, was by one of the windows, light spewing onto him.  As he was fast asleep.  Along with Sehun, who was just staring out the window, with his signature emotional expression.  The other three princes, who were Chen, Kai, Chanyeol; were either dangling their feet off the railing off the top floor or sitting on one of the stairs.  Gathered together, most likely to be planning on doing, something mischief.   

Up until they had heard a knock on the door.  Kris glanced up, from the book that he had been reading, accompanied with a cold face, he said,"Enter."  Without even a hint of a emotion.  The three who were on the top floor, looked down to who had came.  Sehun glanced away from where he was toward the servant.  Lay had woken up, from the knock was looking, with a confused face.  Wondering what had woken him up.  The servant who had previously entered was wearing the entire of the King and Queen's messenger.  The prince's all looked at each other, curious to why their parent's messenger was there.  Though without openly expressing it.

"Speak," Kai said.

The servant had their had head bowed down, aware of all of the princes staring or glaring, in some cases, at them.  As they spoke,"Your Majesties, the Queen and King have sent me with a message. For all of you to go to the throne room, immediately. They had said that it is about mates."  The servant's head still bowed.  Scurried off, after giving a quick bow to all of the princes, left after having given the message that he was sent to deliver.

"Why would our parents tell us to go see them, in the throne room." As Chanyeol was the first to ask.  All were wondering why their parents had asked them, to go to the throne room?  And what it had to do with their mates?

"Let's go, and find out then," Chen said.

All stood up with a nod and left towards the throne room.  Questions were swirling in their minds as if mini tornados in the heads.  Soon arriving at the doors of the throne room, faster then they had actually thought, with all the questions still in thought.  The guards opened up the huge doors of the Throne Room. 

 As they spoke,"the princes have arrived."

The Queen and King had both looked up from what looked like plans for something, that the princes had no knowledge about.  He glanced over at his advisors and the servants, all giving a curt bow, taking their cue, to leave.  Know all well, what was the exact reason, why the King and Queen had called for the princes.  

After the only ones that where remaining, were of the Royal family.  

The King started, "My sons, you all know very well, that in order for your mother and I to be able to pass down the crown.  Is for you to find your mates.  As it has been for previous generations and all generations to come.  After having waited long enough.  Your mother and I have decided that it is time for the Mate Ball.  In order to for you to find your mates.  Since not having found them after years."

"You know that we love you dearly, but we won't be able to rule over this kingdom for forever.  We have to soon pass down the crown.  With you all the age perfect, for ruling the Kingdom.  Only need to have your mates." The Queen spoke in her soft voice.  

The princes knew at too well. They have been in search of their mates, for years. But not have been able to find them. Now having reached the age, to  pass down the crown but are not able to, due to the reason of not having found their mates.  

Kris was the first one to ask, as he was the oldest of the princes.   He calmly asked, "When will the Mate Ball be?"  Having had digested the news the fastest.  While the other's where still wearing their minds about the Ball.  All the princes looked up to their parents, for this answer.

"The Ball will be held within a week, the sooner it is, the faster you will find your mates and descent the throne." The King said.

"A week." All the princes exclaimed except Lay.

"Well, it is true. That the sooner it is, then the sooner we will be with our mates." Lay said, calmly.  

"True"-Sehun said shortly.  As Sehun didn't say much.  Even though, he was the youngest.  All looked at Sehun, he just gave a shrug.  

"Okay, well that's decided.?"  Said Chen.

"Any theme, or what's going to be there?" Kai said.

"Anything to do other than just music, food, and dancing?" Said Chanyeol.  

"Come down, first.  I assume that you all have heard of Exo Circus."  The King said.  Of course, they knew.  It was famous throughout the whole entire kingdom.  All of the princes had been wondering what made it so special.  Having always heard rumors about them.  The six mysteries acts.  That made it so mysteries.   No one even knows who they are because of the masks that they always wear, that hides their identities, from everyone.  But the one thing that is weird is that no one has actually seen the one, in charge of Circus.  Who is usually the ringmaster.  But the Ringmaster was actually one of the mysterious acts.  No one knows, who they are. 

"Yes, we are familiar with them, father." Replied Kris.

"They will be performing in the main Garden, at the Ball and it will be a Masquerade theme."  The Queen responded, happily.

"Go now, your mother and I have some planning to do." The king said.

All the Princes left.  Walking towards the Training room, to help calm their minds.