Feedback incident: trim first part of the thread

Content

Hi All,

If an incident is created from feedback on an incident. Then, customer's message is automatically appended with " This feedback is about:
http://opn-company.rightnowdemo.com/app/answers/detail/a_id/14" as the prefix. I need to show the customer's message in the report, for that i need to trim till the last of the of the standard prefix and show the exact message in the cell. 

Problem is, last part of the string is the answer ID , hence, it is dynamic and it will change for every answer. Even its length will increase with time. How can we trim it dynamically?