Can a disbeliever be regarded as a mahram for his Muslim sister when travelling?

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Check below answers in case you are looking for other related questions:
Who are the mahrams in front of whom a woman can uncover?
What is the khulwah that is forbidden?

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Related Answers:
The father’s (ex-)wife is a mahram to his sons even if she did not bear him any children
Her husband divorced her; is his father still a mahram to her?
Is the son of her husband’s daughter regarded as a mahram for her?
Who are the mahrams in front of whom a woman can uncover?
What is the khulwah that is forbidden?

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