So sorry for your loss.
Be prepared that he may become emotional, many " non emotional guys" do at the loss of their mothers.
Also prepare yourself of talk about wanting to move back to the home country to raise the kids.
Be there with an extra pat on the back a shoulder squeeze, that extra cup of coffee.
If needed help him make plans for traveling for the funeral-if he needs to or wants to stay longer than you can be supportive of that.