One Direction's Louis Tomlinson -- My Kid's Grandma is Down with Me!

Louis Tomlinson had a command performance with someone more important than the Queen ... his baby mama's mama.

We've learned Louis snuck away last month from One Direction's "On the Road Again" tour and flew to L.A. to meet Briana Jungwirth's mom. It appears the purpose of the visit ... to either break the news about Briana's pregnancy or get her seal of approval.

It worked like a charm. Louis, Briana, her mom and little brother spent an afternoon hanging out in West Hollywood where they cavorted with Louis' monkey pal in the "Steal My Girl" video.

We're told Louis made it clear to his baby mama's mama ... he's excited about the baby and promises to be a good dad after Briana pops in early 2016.