Is it obligatory for a woman to wear the hijab in front of her paternal grandmother's brother?

The brother of a woman's paternal grandmother is her father's maternal uncle. The father's maternal uncle is considered a maternal uncle to his daughter, and consequently, a maternal uncle to his daughter's daughter, meaning he is a maternal uncle to the woman herself. He is among her mahrams, and she is not obligated to observe hijab in front of him. She is permitted to uncover in front of him what is customarily uncovered in front of mahrams. Sheikh Ibn 'Uthaymeen affirmed that the paternal aunt and maternal aunt of the father, and the paternal aunt and maternal aunt of the mother, as well as the paternal aunts and maternal aunts of grandfathers and grandmothers, are all mahrams to the woman.