Andy Cohen got choked up on-air Thursday night ... shedding tears for a former employee and friend who died after a battle with brain cancer.

The TV host took on a serious tone during "Watch What Happens Live" ... revealing Kyra Samson -- a former production manager for Bravo -- died Tuesday at 28.

Andy said Kyra spent 4 years with Bravo and was "known for her sweet smile and gentle demeanor" ... though she could also use her mighty voice to corral huge BravoCon crowds when necessary.

He said Kyra will be terribly missed by everyone at the show and everyone who knew her ... encouraging folks donate to a fund set up in Kyra's honor, which will benefit cancer research. The fund is nearing $300,000 out of a $350K goal as of Friday morning.

Andy finished off his message by saying the thoughts and prayers of everyone at Bravo are with the Samson family.

Kyra's father -- podcaster and former Miami Marlins President David Samson -- posted about her death Wednesday ... telling followers she passed away after a 9-month battle with glioblastoma, a type of brain cancer.

He wrote, "While her life got stolen from her, she handled these months with courage, poise, and resolve. And all I want is for no family to feel what we feel today. For no young person to suffer the way she did.”

RIP