Did you not get all the finances sorted out at time of divorce? He could make a claim against you regarding your pension if you did not get a Consent Order at time of divorce. Did you not get legal advice at time of divorce?
He could be entitled to a pension share based on how many years you were together and it will always be in the form of a percentage. Did he not have a pension? Did you not have any assets? In order to determine what share he would get depends on many factors, some of the above i have already asked you? You need to be more specific about what happened at the time of your divorce. He will no longer be entitled to a widows pension as you got your divorce absolute. But they can argue that he should get more then because he has lost certain benefits ect.
Like i say if you can post more information then someone can answer you more correctly.