Limestone and Marble have always lived on the farm, but once Pinkie and Maud left, they realized how lonely they were. Marble’s heart had been broken when she realized Big Mac was in a relationship, while Lime was too crude and aggressive to attract anyone she liked. That’s when they turned to each other for comfort.
 
Their relationship was entirely mutual, but it wasn’t a romantic one. They just wanted to feel loved by someone, even if it was just physically. They kept this arrangement to themselves, unsure how their family would react. That was, until, Limestone got pregnant.
 
Lime kept this revelation to herself for a couple of months before telling Marble. They were terrified, unsure exactly how it happened or how they would explain this to their family. Lime decided she needed to carry out her pregnancy away from their family, and left for Canterlot. She told them it was a vacation, to rest her hooves and recuperate.
 
When she finally gave birth, Marble was right there beside her the entire time. They named their daughter Chalcedony Bedrock Pie, and decided that instead of revealing the true nature of how their daughter came to be, Marble would “adopt” and bring her home.
 
Chalcedony is a soft spoken filly who is aware of who her parents really are. And while they both love her deeply, this doesn’t stop her from thinking she’s disgusting and shouldn’t even exist. Chalce (pronounced Chelsea) is currently living with Marble and her wife Fluttershy, and is now a big sister to three little fillies. Overall, she’s a nice, sweet filly. She’s terrified if her friends, her family, and her new step-mom ever found out how she came to be, they would look at her with disgust and vitrol.
 
Lime also constantly writes letters from Griffinstone, where she’s married to Lady Gilda the leader of griffins. She loves her daughter, despite how she came into her life. She misses her dreadfully and takes any chance to have Chalce visit or vice-versa.
 
Despite their past, they’re all happy with their lives now. Let’s just hope no one gets suspicious.