I've looked into this for a friend and it seems if your Fiance had no will then his estate will go to his next of kin, which could be any member of his family, it doesn't matter if he never saw them.
Even if you had children together, you still have no rights as a cohabiting partner. If you lived in Scotland this would be different, but a similar bill in England, giving cohabiting couples the same rights as married ones, was thrown out a couple of years ago.
I was supposed to be getting married to my Fiance at the end of the month, but due to bereavement, we will be postponing the wedding. I'm due to have our baby in June and I've insisted we both have wills written, otherwise in the event of either of our deaths, we have no rights to each others property. His will go to his mother and mine to my estranged sister.
You should get legal advice asap.