Molli's mama -- who memorably welcomed her firstborn during the fourth season of 16 & Pregnant -- excitedly shared her life-changing news on Instagram. And fittingly, Katie's mini-me is front and center in the baby announcement.
"Sometimes being a big sister is even better than being a princess," the Wyoming native captioned the image above, featuring the smiling kindergartner reading a book entitled Little Miss, Big Sis. "March 2017 #babythayn," Katie added.
Soon after the congratulatory messages flowed in, Katie offered some more details about the baby's father and why she has kept her personal life private since chronicling her life on MTV.
"I've been with a wonderful man for over a year," she wrote. "The sign of a happy relationship is no sign of it on social media. Even if I was single, it would still be a blessing. I've been a single mom to Molli most of her life, and she is amazing."
Be sure to offer your well wishes to Katie and her family in the comments -- and for an old-school rewind, relive Katie preparing for the arrival of Molli in the 16 & P clip below!