Search and Replace Pattern

Using structual search and replace I am trying to write a regex to substring an identifier but with no luck

my identifier regex is

$HANDLE$ = \b(_\w+|[\w-[0-9_]]\w*)

and what I am trying to perform with this is to isolate


OnOpenOpportunity from Me.OnOpenOpportunityEvent

using the pattern Me.$HANDLE$ matches the whole identifier as expected
using the pattern Me.$HANDLE$Event does not match anything

I've also modified the identifier regex to $HANDLE$ = \b(_\w+|[\w-[0-9_]]\w*)Event but that matches the whole identifier.

Any ideas?