Brett Gardner -- former star of the New York Yankees -- has just announced the death of his 14-year-old son ... adding it came suddenly after he became ill along with a group of family members on a trip.

The 14-year MLB veteran and his wife, Jessica, announced the news in a heartfelt statement, released through the Yankees social media channels ... explaining their son Miller passed away Friday.

According to the Gardners, Miller and a group of other family members got sick while on vacation ... adding they have far more questions than answers at this point.

Brett & Jessica write Miller was a "beloved son and brother" who competed in a number of sports and enjoyed spending time with friends and family.

They add their thanks to those who have reached out to offer support and encouragement ... and, they're asking for privacy at this time.

Brett and Jessica share one another child, a boy named Hunter.

Brett played his entire career with the Yankees from 2008 to 2021 ... appearing in 1688 games with the Bronx Bombers. He was an All-Star in 2015, won a Gold Glove in 2016 and was a part of the last Yankees team to win a World Series in 2009.