Praise be to Allah.
A Muslim is not permitted to inherit anything of the wealth of a non-Muslim relative, as the Prophet (Peace and Blessings of Allah be upon him) said: "The believer does not inherit from a kaafir (disbeliever) and the kaafir does not inherit from a believer." (Reported by al-Bukhaari, al-Fath 4283). According to another report, he said: "The Muslim does not inherit from a kaafir and the kaafir does not inherit from a Muslim." (al-Bukhaari, 6764). The Messenger of Allah (Peace and Blessings of Allah be upon him) also said: "People who belong to two different religions do not inherit from one another." (Reported by Abu Dawud in al-Sunan, Kitab al-Faraa’id, and deemed hasan by al-Albaani in Saheeh al-Jaami‘, 7614) - because when the ties of religion are cut, the ties of inheritance are also cut, because the former is the basis of the latter.
However, if a non-believer makes a will leaving one-third or less of his wealth to his child (son or daughter), one is entitled to take it, because this is a will as opposed to inheritance according to a non-Islamic system. This difference is well-known in Islamic fiqh.
And Allah knows best.