Passage: Henry Daniel Mills is a fictional character in ABC's television series Once Upon a Time. Henry is the boy Emma Swan gave up to adoption; Regina Mills adopted him. Henry was first portrayed as a child by Jared S. Gilmore, who won the Young Artist Award for Best Performance in a TV Series -- Leading Young Actor in 2012. Starting with the seventh season, Andrew J. West will take over the role of Henry as an adult and father to a ten-year-old girl named Lucy.

Question: Based on this passage, henrys last name on once upon a time?
Steam of consciousness below:

The relevant information is: Henry Daniel Mills is a fictional character in ABC's television series Once Upon a Time.
So, the answer is Mills.