Starfish's point was good, that his mom helped make him who he is.

Depending og how close he was to his mother and his own personality, he may not grieve that openly or want to share much. But he will feel the loss a lot more around holidays and typical family events, especially the first year. Remembering to ask him how he's doing around times like these, when everybody else has stopped asking, is maybe one of the most thoughtful things you can do to help.