THIS IS NOT THE FLAG OF THE PRINCIPALITY OF ROMANIA! The Principality of Romania used the standard Romanian tricolor.Flag of the Romanian Army (1872 - 1921), official model. The 1872 law regarding the Romanian flag states that the Army one will have the country's coat of arms in the middle of the tricolour. Instead of the official model, there were other flags used (see below).

This was also the princial/royal standard until late XIXth century.
Own work
Alex Daneş