A 17-year-old boy in the Netherlands woke up from routine knee surgery speaking only English, not his native Dutch. Nurses first thought this unusual behaviour would pass. It did not. The teen insisted he was in the United States and could not understand or speak Dutch. Doctors later called this rare condition foreign language syndrome (FLS), where patients suddenly switch to a second language. The surgery was successful, and the boy had no prior psychiatric issues. A psychiatric check found him calm and cooperative, but he spoke only English with a Dutch accent. After 18 hours, he could understand Dutch but struggled to speak it. The next day, friends visiting helped him regain his Dutch language fully. Doctors decided no further brain tests were needed. He left the hospital three days after surgery. Foreign language syndrome is very rare, with only about nine cases recorded before. Most involved similar total switches to another language, usually learned later in life. This may be the first known adolescent case. The cause is unclear but might be linked to anesthesia’s effects on the brain. The condition is usually short-lived, with full recovery and no lasting damage.