Kylie Jenner Buys Third House

Kylie Jenner's dropping millions to make herself a bonafide real estate mogul ... unlike most other 19 year olds who have to drop cash on college tuition and school books this time of year.

TMZ has learned Kylie closed on another Hidden Hills, CA property Tuesday. The 4 bedroom, 4 bath home set her back around $4.5 mil and is right next door to the $6 million pad she purchased in May.

She also owns a property in the nearby gated Calabasas community where most of her fam lives -- but that was just her starter home. She's listing it for $3.9 million, if you're keeping tally.

The plan is to use the new place as work space for her growing cosmetics line, and as a crash pad for friends ... aka Tyga's very expensive doghouse.

The 5,000 sq. foot home has a pool and jacuzzi ... like most home offices.

Kylie's agent, Tomer Fridman, wasn't available for comment, but Kylie gave a glimpse inside via Snapchat after she got the keys.