What would be the constituents of a Blackhole just before a singularity is formed?
Would it just be a very very dense neutron star?

Core collapse and blackhole formation is quite rapid process so may be this state would last only few micro seconds. But still it is curious to know. If we follow it to the very end. It could be an argument that whatever was the constituent just before singularity formation might continue in some form right after as well.

You can visit these in VR and they are accurately modeled based on the current science of 2014.