Complex sentence: Hunt had begun his education at the Boston Latin School, but after the family's move to Europe Hunt entered the atelier of Hector Lefuel in 1846 and became the first American architect to attend the École des Beaux-Arts in Paris.
Split into simpler sentences: Hunt had begun his education at the Boston Latin School, but after the family's move to Europe Hunt entered the atelier of Hector Lefuel in 1846. The young aspiring architect became the first American to attend the École des Beaux-Arts in Paris.