It was only a matter of time before this got nasty!

Louis Tomlinson has lawyered up and is preparing to wage a custody war against baby mama Briana Jungwirth, who he believes is using their newborn son Freddie Reign to get more money, TMZ reports.

The One Direction hunk is already paying the single mother a significant amount in child support, and went so far as to buy her a three bedroom home in Calabasas, but he claims she's withholding visitation of their little one until he coughs up more dough.

This is what happens when you have a one night stand!