Queen of Love and Beauty

Queen of Love and Beauty is a tradition in the Seven Kingdoms.

Season 4
In Ser Duncan the Tall's entry in The Book of Brothers it mentions that he named a commoner as the Queen of Love and Beauty after winning a tournament at Pennytree which King Aegon V Targaryen held in his honor.

In the books
In the A Song of Ice and Fire novels, the tradition holds that the victor in a tournament may select any woman present and name her the queen of love and beauty, crowning her with a wreath of flowers and dedicating his victory to her.

The victorious knight often chooses a woman he loves or intends to court, and it can be a source of scandal if the victor crowns a woman already bound to another man, or if a married man crowns someone other than his wife. Since both of these cases were true when Prince Rhaegar Targaryen crowned Lyanna Stark after winning a tourney at Harrenhal, it was particularly scandalous.

Queen Naerys Targaryen was crowned by her brother Prince Aemon the Dragonknight, who was disguised as a mystery knight known as the "Knight of Tears".

Princess Rhaella Targaryen was crowned by Ser Bonifer Hasty.

Ser Jorah Mormont crowned Lynesse Hightower after winning a tourney at Lannisport, requesting and receiving her hand in marriage from her father that very night.