Remove all characters in a string until a substring is matched

Hello all,

How do I remove all characters in a string (filename) until a substring is matched.

Let's say:

Filename = "abc123 MP3Tag Filename"
Filename = "abcdef123 MP3Tag Filename"
Filename = "abcdefxxx123 MP3Tag Filename"

substring = "123"

Filename will become "MP3Tag Filename"

Thanks for your help.

Create an action of the type "Guess values" for _FILENAME
Guessing pattern: %dummy%123 %_filename%

Or use the Convert>Filename-Filename function:
Source: %1123 %2
Target: %2

Additional to the working proposals from user 'ohrenkino' in post #2.

Remove all characters from the left side of the filename string ...
until and including the last character of the search substring.

From: 'abcdefxxx123 MP3Tag Filename' 'abcdef123 MP3Tag Filename' 'abc123 MP3Tag Filename' To: 'MP3Tag Filename' Action "Format value" Field ......: _FILENAME Formatstring: $cutLeft(%_filename%,$add($sub($len('123 '),1),$strstr(%_filename%,'123 '))) ... or ... Formatstring: $cutLeft(%_filename%,$add(-1,$len('123 '),$strstr(%_filename%,'123 '))) ... or ... Formatstring: $mid(%_filename%,$add($strrchr(%_filename%,'123 '),$len('123 ')),$len(%_filename%)) ... or ... Formatstring: $reverse($left($reverse(%_filename%),$sub($strstr($reverse(%_filename%),$reverse('123 ')),1))) ... or ... Formatstring: $regexp(%_filename%,'^.*123 (.*)$','$1') ... or ... Formatstring: $regexp(%_filename%,'^.*123 ',)

DD.20150928.1952.CEST, DD.20150929.0710.CEST

I've tried with Convert>Filename-Filename function, it works well.
Thanks for your help.

I've used $cutLeft(%_filename%,$add($sub($len('123 '),1),$strstr(%_filename%,'123 ')))
It works wonder for me.
Thank you VERY VERY MUCH for your quick help.

Cheers