Fimmilena was a Time Lord. She disguised herself as Queen Boudicca of the Iceni, where she married King Prasutagus and had two daughters, Alaina and Nicola.
Prasutagus was mortally wounded fighting the Romans, and "Boudicca" accepted the help of the Fourth Doctor and Romana I. "Boudicca" was injured in the fighting, recovering in the Doctor's TARDIS while Romana took her place.
The Iceni lost to the Romans, and the dying Fimmelena, with her daughters already dead, entered her TARDIS, which was disguised as one of the Stonehenge stones, and regenerated. (PROSE: Good Queen, Bad Queen, I Queen, You Queen)