A female relative stumbled on the grisly scene inside the bloody Cypress Hills home in the afternoon, finding Roosevelt Simmons, 91, and his daughter Jacqueline Delyons, 66, dead, sources said.

The relative told cops that Deylons’ 46-year-old boyfriend was also inside the home and told her, “You know what happened,” sources said.

Eric Brooks, who’s Simmons’ grandson and nephew to Delyons, told The Post that his stepmother was the woman who made the grim discovery.

Sources said the boyfriend has been taken into custody as a person of interest but has not charged in the senseless killing.

“He’s been with my aunt for over 20 years,” Brooks said of the beau. “I don’t know if he still lived here.

“[He] was quiet, wasn’t aggressive, as far as I know. … We want answers, no one knows what happened.”