Portrait Paiting Artist Unkown Age Unknown Everything Unknown

Hi there, I have recently come into ownership of this beautiful painting. I do realise it's old and have been told it came from a very expensive source but beyond that I do not have any information . I have taken the painting out of the frame to see if there is a signature (there isn't) and I have no real clues over how to start the process of finding out who painted it or how old it is. Can anybody help.