Conrad Hilton — Checked Into Rehab After Mid-Flight Tirade

EXCLUSIVE

Paris Hilton‘s little brother got his ass into rehab almost immediately after he allegedly went nuts on a British Airways flight last summer … TMZ has learned.

Conrad Hilton appeared in court today after surrendering to authorities investigating a bizarre incident. We broke the report … 20-year-ancient Hilton allegedly berated and threatened the crew during the July, 2013 flight from London to LAX.

Conrad told feds…