I thought it was just another leaf growing, but to my surprise it was a bloom stalk. It lasted less than 24 hours before expiring, and a second opened up. It's always cool to get surprise blooms!
Isn't that a Ctenanthe amagris (prayer plant) instead of a Calathea?
I recommend everyone to plant that thing into LECA. Mine thrive like weeds and are blooming multiple times a year.