It seems I was right.He is of Mexican descent...
Royal Musings: Tatiana Galitzine weds Guillermo Sierra
He was born there.
He is not of Mexican descent. He is a Mexican. I do not know if he is a US citizen. He had a student visa when he attended Wharton. Got his green card shortly after his marriage to Emily Hilton. They divorced in June of 2015. They have a son.