The doors slam open and Princess Cadence runs through. "Aunty!" she shouts. 
"Cadence, you came. I was worried you wouldn't make it in time."  
"What's going on?" She rests a hoof on the side of the throne. 
"This is a horrible idea." Luna mumbles, "This is wrong." 
"I wish to tell you that... I'm expecting a child." she explains with a half smile. Cadence jumps back. "I know this is sudden, but everything will be explained at the announcement shortly." 

Celestia, Luna, Cadence, and Twilight stand before the ponies of Equestria. "My little ponies. I figure you question why i summoned you here." Celestia begins, "I will tell you. For I, Princess Celestia, Riser of your sun, am expecting..." She pauses for a moment then continues, "An heir to the throne!" 
The ponies cheer. Celestia smiles. "But you must know this! You will accept them! No matter what they are! Princess Twilight Sparkle, Princess of Friendship, will adopt this child!" The ponies mumble in confusion. "I cannot care for a child while watching over the kingdom. The child must not know I am their mother. That will be revealed on their 18th Birthday." The ponies cheer in agreement to never tell the child.