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 he had taken a sleeping pill before boarding the plane … which his attorney Robert Shapiro says could have caused the outburst.

Sources connected with the Hiltons tell us … right after the incident … Conrad voluntarily tartan into a 30-day inpatient drug and alcohol treatment program.

Hilton was released on $ 100,000 bail today at today’s hearing. He was ordered to surrender his passport and remain in California.