Take context from the input text and decide on the accurate relationship between 'St George Bank' and 'Westpac' from the options provided.
Options: position held, location of formation, stock exchange, parent organization

Mrs Kelly was chief executive and managing director of St George Bank from 2002 to 2007 and CEO of Westpac from 2008 until early this year, overseeing a merger of the two banks in 2008.
parent organization