The kitchen wiz -- who appeared on the third season of the reality show -- passed away last week, which was made public in a local obituary. Howard's mother told the Miami Herald, "I am just finding out how many lives he touched. He was married to his passion in life, which was his cooking."

She also confirmed he'd suffered a heart attack.

Bravo addressed Kleinbeg's death as well, writing ... "The Top Chef family is saddened to learn about the unexpected passing of Howard Kleinberg from season three. Howie’s passion for cooking filled so many and our deepest sympathy goes out to his family and friends."

HK is best remembered for competing in "Top Chef: Miami" in 2007, where he placed seventh. Afterward, he opened his own restaurant in town called Bulldog Barbecue -- among other eateries as well -- and found success in the local scene.

It was actually a memorable run for Kleinberg -- with one of his highlights from that season being a tense conversation he had with the late Anthony Bourdain, who was chastising him over speed in the kitchen ... only to have the tables turned on him by Howard dropping a Bourdain quote from one of his books, which left AB thoroughly impressed.

Kleinberg is survived by his mom, his stepdad, his sister and her children. He was 46.