Open Question: Shell Casualty Co. insures Bob under a PAP and also insures Ted under a seperate PAP. Bob and Ted were involve?

Shell Casualty Co. insures Bob under a PAP and also insures Ted under a seperate PAP. Bob and Ted were involved in an auto accident when Bob ran a red light and struck Ted's car. Shell paid damages to Ted under his collision coverage. Shell then sent Bob a notice of intent to subrogate. Bob denies that he has any liability to Shell. Shell argues that Bob is liable to it for its payment to Ted