Manhattan prosecutors will begin presenting murder charges to grand jurors today in the Soho House slaying of tragic designer Sylvie Cachay, The Post has learned.

Accused killer ex Nicholas Brooks — the stoner son of rape-scandal-scarred, Oscar-winning composer Joseph Brooks — is not expected to testify on his own behalf to fight the murder case being mounted against him in a lower Manhattan grand-jury room, a top investigative source said.

Brooks is being held in a Queens jail pending his court date tomorrow, when he will learn whether he has been indicted in his former girlfriend’s death.

Defense lawyer Jeffrey Hoffman — who represents both the father and son — and the elder Brooks both declined comment yesterday morning as they left Manhattan Supreme Court. The “You Light Up My Life” composer was there for a hearing on his own criminal matter.

Thirteen women accuse Joseph Brooks of casting-couch assaults in his Upper East Side apartment, with nine of them saying they were raped.

Meanwhile, a somber wake for Cachay, 33, was held throughout the afternoon in a Virginia funeral home bedecked with flowers and dozens of photos showing Cachay smiling and enjoying life with friends and family.

Additional reporting by Grant Slater in Vienna, Va.