An Instagram on Mugler's official page went up Sunday with the tragic news. It was a photo of nothing but a blank square, with the caption ... "#RIP We are devastated to announce the passing of Mr Manfred Thierry Mugler on Sunday January 23rd 2022. May his soul Rest In Peace." The same message was repeated in French as well.

No word on a cause of death, but his passing seems sudden and unexpected -- as he didn't appear to be ill or battling any known ailments.

As you can imagine, the tributes started to pour almost instantly ... especially from folks in the fashion world, who knew Mugler well from his decades-long work and influence in the industry.

It goes without saying ... Mugler has dressed some of the biggest names in the game, including Kim Kardashian -- whom he actually graced with an outfit of his during the 2019 Met Gala, this after he'd officially retired -- plus a plethora of other models and stars.

His extravagant designs have been fan-faves among celebs like Lady Gaga, Cardi B, Jerry Hall, Beyonce, Katy Perry, Rihanna, David Bowie, George Michael, Linda Evangelista, Demi Moore, Megan Fox, Miley Cyrus, Madonna, Cindy Crawford, Tyra Banks, Sharon Stone, Diana Ross, Nicole Kidman, Reese Witherspoon, Robin Wright, Bella Hadid ... and many others.

All of them have donned Mugler-designed getups at one point or another, be it on the red carpet, on the runway ... or on stage. The guy's work touched at least 3 different decades of fashion -- and he was absolutely beloved among Hollywood's finest.

In addition to his clothing contributions, Mugler also left his mark in the fragrance biz ... with a diverse line of perfumes that are still best sellers to this day.

He was 73.