Sources close to Chris' family tell TMZ ... he died Thursday afternoon at 1:45 PM from a heart attack. We're told Chris had been in and out of the hospital for the last year, but the heart attack came as a surprise to doctors and relatives.
Despite his medical battles -- related to a nasty fall he suffered 2 years ago -- we're told Chris was still designing dresses until the end.
Chris was a finalist on season 4 of "Project Runway" ... he also appeared on "Project Runway All Stars" and had his own show on Bravo called "Mad Fashion." He also made cameos on "The Real Housewives of New York City" ... helping find elaborate costumes for Sonja Morgan.
Known for his avant-garde style, Chris had major A-list clients. He designed for Madonna, Lady Gaga, Jennifer Coolidge and, as we said, Bey and Streep. He was responsible for Meryl's 2010 Golden Globe and Oscars gowns.
Chris also designed costumes for Cirque du Soleil and a slew of Broadway performances.
He had struggled to fully recover from a June 2017 fall in his apartment where he'd hit his head. Chris laid there for 4 days, finally woke up and called 911 before being rushed to the hospital.
He had to be placed in a medically induced coma, and suffered organ failure ... including a collapsed lung.
Chris was 56.