Goddesses of the Mabinogion

Branwen

Branwen,the daughter of Llyr who was given to Matholwch,a High
king of Ireland in marriage.  When her brother Efnissien insulted
the King he forced her to forsake her title as Queen  and sent her to 
work in the castle kitchens for three years.  Branwen befriended a 
starling and sent it to her brother Bran in Wales with a message
of her imprisonment.

Bran led a fleet across The Irish Sea to rescue his sister.
In the ensuing battle Efnissien killed Branwens son Gwern.
  
When she saw the destruction caused because of her, she died of a broken
 heart.  She was buried on the banks of the river Alaw in Anglesey.
The river then became known as Ynys Branwen.