C# RegExp for search inner pattern

I have a string like this

[[[a]]][[[b]]][[[c]]]

I want to extract these :

a
b
c

So i wrote following Pattern :

@"\[\[\[(.+?)\]\]\]"

It works but the result is :

[[[a]]]
[[[b]]]
[[[c]]]

What is the matter ? could you help me ?

Thank you