Louis Tomlinson: Picking 1D Baby Name Was a Fair & Balanced Fight

Louis Tomlinson's newborn son's name was the first adventure in co-parenting for him and baby mama Briana Jungwirth.

As we've reported, the kid's name is Freddie Reign Tomlinson and our One Direction source tells us Louis picked out the Freddie part, while Briana came up with the royal-sounding middle name.

No rhyme or reason for Freddie, we're told Louis just liked the ring of it and Briana didn't object.

As for Reign, we're told Briana wanted something earthy, but thought Rain sounded too girly ... so she went with the more kingly version.

It's all fun and baby names -- until diaper duty starts.