Name: Sailor V no Joutai wa Princess Datta no! [Sailor V's True Identity was the Princess!]
Original Air Date: December 20, 2003
Director: Masataka Takamaru
Writer: Yasuko Kobayashi

Important Plot Points:

Sailor V announces she is Princess Serenity as well as Sailor Venus

First use of the Venus Beam attack

Zoiste realizes Tuxedo Kamen is Endymion

Zoisite turns into a stone