Johnny Strange -- Famed Adventurer Dies At Age 23 ... Wingsuiting Accident

Johnny Strange -- who became famous for climbing the world's 7 tallest summits by the age of 17 -- has died in a wingsuiting accident in Europe ... TMZ Sports has confirmed with a family member and multiple people close to him.

Multiple sources connected to Strange tell us Johnny was in Switzerland -- where something went wrong during his jump ... and Strange was killed as a result.

Strange called in to "Kevin & Bean" on KROQ on Monday from Switzerland and said he was shooting a dangerous wingsuit proximity video where "we fly super close to stuff."

After the K&B interview, Strange shot a video doing some wingsuiting, which he posted to social media.

Johnny made national headlines as a teen -- appearing on "Conan O'Brien", CNN and CBS News when he became the youngest person to ever climb the "7 summits."

Strange climbed his first "world class peak" when he was 12 -- conquering Mt. Vinson Massif in Antarctica. Since then, he traveled the world doing extreme sports ... including base jumping into the Grand Canyon.