Hay quit this week but will continue to work with the company as a non-executive director.
Brighter co-founder Remy Blumenfeld will stay on full-time as creative director but it is unclear how long for. He and Hay were both locked into earn-out deals after selling Brighter to Endemol four years ago but those contracts have since expired.
Endemol plans to continue the Brighter Pictures brand and has brought on board executive producer Elaine Hackett to run the company with Blumenfeld. Her remit will be to expand the indie's factual entertainment slate.
Her credits include exec producing Channel 4's Teen Big Brotherand Five's Cosmetic Surgery Live.
Blumenfeld said in a statement: "This announcement signals the next chapter of creativity and growth. Elaine is someone who can execute big and complex ideas without losing sight of detail."
Hay and Blumenfeld set up Brighter in 1992 and sold the company to Endemol UK in 2001 for an estimated£10m. Last year Brighter posted£1.7m profit from 350 broadcast hours, which included long-running lifestyle show Get a New Life for BBC2, Tabloid Talesfor BBC1 and controversial dating format There's Something About Miriamfor Sky One.