Also, huh... rechecked the usual keiba places and found a weird inconsistency. Most of them mention she has eleven foals, with the 11th born in 2021 being her first son. Shadai Farm also mentions so. But JBIS contradicts the other sources by listing an unnamed filly born in 2016 to King's Best (making her 2021 foal the 12th). This filly is conspicuously absent in other sources.
Oh well, going with Shadai Farm's version of events then. Eleven foals, first ten all daughters. That's what most of the horse fans go with anyway.
(Personally though, can't quite get rid of the nagging feeling that the 2016 filly passed away early or something so they didn't count her...)