Walsh, a 36-year-old singer and music producer, announced in an Instagram Story message on Monday that he and Siriano split after nearly two years of marriage.
"Bit more than a month ago my husband and I separated," he wrote. "I was contacted by a writer for a website who somehow found out, so rather than let them break it, I'm telling you myself. It's nobody's business and I don't want to discuss, but that's what's up."
A rep for Siriano also confirmed the news. "I can confirm they’re separated," his rep told ET in a statement. "They were together for 11 years, love each other very much and request privacy at this time."
Siriano and Walsh tied the knot in Danbury, Connecticut, in July 2016 after getting engaged in 2013. A slew of celebrity guests attended the wedding, including Jackie Cruz, Jay Manuel, Alicia Silverstone and Kelly Osbourne. Rather than wearing traditional rings, the couple wore matching engagement bracelets.
The two started dating in 2007, just prior to Siriano winning season four of Project Runway. In May, Siriano and Walsh were still attending events together, including the Time 100 gala in New York City.
That same month, ET got an exclusive sneak peek at the the costumes that Siriano designed for Sugarland's upcoming tour. Check it out: