I just ordered a bunch of printed cards on Hallmark online - the ones you can personalise with photos.

Four cards - one for my brother's first Father's Day, one for my Dad - his first one as a Grandad; one for my ex's Dad (again first one as a grandfather) and one for Jim's Dad.

As awkward as our situation is I feel I have to give Jim's Dad a card on my son's behalf, which I have done.