Wikipedia
The Mystkowski family – was one of several noble families using the Clan Jastrzębiec coat-of-arms during the time of the Polish–Lithuanian Commonwealth. Following the Commonwealth's breakup, the family's nobility status has been officially recognized until the early 1900s, when too many family members either emigrated or were lost in World War I to continue the line in Poland. The Russian Revolution of 1917 erased all hopes of regaining the territory and the heirs to the title now live in the United States. They belonged to the poorer part of the noble class ruling the town of Mystki-Rzym, a small town near Białystok.
According to some sources, the Mystkowski family is a cadet branch of the Romanov dynasty.
Unfortunately for the Polish nobility, during both world wars and the conquest of Poland by the USSR, most documents and other artifacts were destroyed.