The 14-year-old son of former New York Yankees outfielder Brett Gardner died from carbon monoxide poisoning while vacationing in Costa Rica last month, according to the country’s Judicial Investigation Agency. Miller Gardner passed away peacefully in his sleep on March 21 after he and family members became ill during their trip.

Toxicology tests revealed Miller had a carboxyhemoglobin saturation level of 64%, well above the 50% threshold considered lethal, said Randall Zúñiga, director of the investigative agency. No drugs were found in his system. Authorities detected high levels of carbon monoxide in the hotel room where the family had been staying, contradicting earlier suspicions that food asphyxiation was the cause of death.

Miller Gardner.

Miller, the youngest of Brett and Jessica Gardner’s two children, was remembered in an obituary as deeply loved by family, friends, teammates, and coaches. “The void Miller’s passing leaves… will be felt for years,” it read. “The Gardner family will forever cherish the places they visited, the people they met, the friends they made, and the memories they created together.”

Brett Gardner played 14 seasons with the Yankees and was part of their 2009 World Series–winning team.