Should we tell our nephew about his inheritance?

Every week a Guardian Money reader submits a question, and it's up to you to help him or her out – a selection of the best answers will appear in Saturday's paper. This week's question My sister left her husband when their son was a baby. Her ex died four years ago leaving the son quite a lot of money. The problem is my comfortably-off sister used some of it to pay off their mortgage. The son now faces having to give up university for lack of funds. We're angry, but my sister won't discuss it. He's unaware of his inheritance. Do we tell him? What are your thoughts?