Blanche of Castile served as regent of France on two occasions and held great power in the country even when she wasn’t ruling.
Blanche of Castile: France’s Indomitable Regent

Blanche of Castile served as regent of France on two occasions and held great power in the country even when she wasn’t ruling.
Rosamund Clifford (c. 1150 - c. 1176) was Henry II of England's mistress. Unluckily for her, his wife was Eleanor of Aquitaine, who was not at all fond of The Fair Rosamund.
Berengaria of Navarre became Queen of England in the 1100s, but because her husband was always on crusade, she never got to settle down in England.