How to add last word to %Artist% tag by guessing_pattern

Hi, this is my filename:
Artist1; Artist2 - Title [Artist3].mp3

I want to add Artist3 to %Artist% tag to have:
%Artist%: Artist1; Artist2; Artist3
%Title%: Title

I have tried this guessing_pattern:
%artist% - %title% [%artist%]

But it only returns me the last %artist% (artist3) and I want all of them (artist1; artist2; artist3). Should I use other action?

I am Sorry for my bad english. Thank you

If you rename the filename ... for example ... using replace ... from ' - ' to '; - ' ...
from: Artist1; Artist2 - Title [Artist3].mp3
to: Artist1; Artist2; - Title [Artist3].mp3

... then you can apply ...
Convert: "Filename - Tag"
Formatstring: %artist% - %title% [%artist%]
... and the result will be ...
ARTIST=Artist1; Artist2; Artist3


Thank you, I've tried this way and it works!