Question Summary:
Is it the ligitimate sons resposibility to look after this child ( he is 20 years of age ) or must he look after himself?

Question Detail:

The father had an affair and a child was born from this affair , the farther falls ill and cannot look after the illigitamate son.
Is it the ligitimate sons  resposibility to look after this child ( he is 20 years of age ) or must he look after himself?

Answer :

In the name of Allah, Most Gracious, Most Merciful
Assalaamu `alaykum waRahmatullahi Wabarakatoh

In principle, when a person is fifteen years and older, he is regarded to be an adult in Shariah. An adult is responsible to take care of his own needs.

However, if an adult experiences difficulties in fulfilling his needs, any assistance rendered to his will be an act of great virtue and reward.

As Muslims, our focus should not be on the rights but on the pleasure of Allah and reward.
And Allah knows best
Wassalam
Mufti Ebrahim Desai
Darul Iftaa, Madrassah In'aamiyyah