Slightly less than 1,500 years ago...
"Where is Estella, dear sister?"
"She says that she is going into the Everfree Forest to forge a weapon for us to use against Discord."
"But in her condition..." Luna gasped. "NO!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!" She turned and took flight. Celestia spread her wings and followed her.
"Estella..." Luna collapsed over her body, sobbing in tears.
Estella stirred, her green eyes opening. "Luna..." She attempted to spread her wing, but the base was rapidly turning to stone, freezing the wing in place.
Celestia came and landed, her eyes locked on the tragedy unfolding in front of her. "Estella, what have you done?"
The elder alicorn smiled, even as her torso turned into marble at an alarming pace. "I have created focui for some of the greatest virtues and attributes that ponykind knows. I call them the Elements of Harmony."
Celestia's normally stern face had tears streaking down her cheeks. "But the curse..."
Estella turned her head and nuzzled at Luna, who was now cradling her in her forehooves. "We all know that it is essentially irreversible. I have used my magic to create a weapon that you and Luna can wield against Discord, in due time."
'No..don't leave us", Luna begged. By this time, the wave of stone had reached Estella's neck.
Estella smiled. "Take care of the sky for me, my youngest sister." Then the magic wave swept through, and Estella's smile was locked in stone.
NOOOOOOO!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Luna screamed, and the sound pierced to the depths of Celestia's anguished heart.