Regex: Remove all match plus one char before all

[Alfalfa]

Hello,
I made this script to find all "|BS|" blocks in a string, and simulate a backspace, as if the string would be typed in a linetext input field. I came up with this:

#!/usr/bin/python3
import re

if __name__ == '__main__':
    string = "it |BS||BS||BS|this is one|BS||BS||BS|an example" #|BS| as in Backspace
    while re.search("\|BS\|", string):
        array = list(string)
        for m in re.finditer("\|BS\|", string):
            del array[m.start():m.end()]
            if m.start()-1 >= 0:
                del array[m.start()-1]
            string = ''.join(array)
            break
    print(string)

which output "this is an example"

It works, but feels very inefficient and I would like to improve it, avoiding the needs for an array or using a single pass regex. I looked at the documentation for re but yet I could not find a satisfying answer. Hopefully you can give me some tips 

Thanks!