Jubilant Sykes — a Grammy-nominated opera singer — was stabbed to death inside his L.A. home Monday — and his son was arrested in connection with the murder, according to police.

Cops said they responded to an “assault in progress” Monday night at Sykes’ Santa Monica home after receiving a 911 call from an unidentified person.

When officers arrived, the 911 caller directed them inside the residence, where they found Sykes with “critical injuries consistent with a stabbing,” police said. Sykes later died at the scene.

Police said his 31-year-old son, Micah, was present inside the home and arrested in connection with the murder, then booked into the L.A. County jail for suspicion of murder. He’s being held on $2 million bail.

“Jimmy Neutron” star Jeff Garcia is in the hospital … and it doesn’t sound good.

Family sources tell us Jeff is currently hospitalized in Southern California, but it’s unclear what is ailing him.

We’re told Jeff was previously hospitalized around November 20 with pneumonia … but he recovered and was discharged a few days later.

His “Jimmy Neutron” character even got his own spinoff show, “Planet Sheen,” in 2010, and Jeff did voice work in 26 episodes.

Jeff’s also a standup comic … and he had been doing comedy work as recently as November … a couple weeks before he wound up in the hospital.

He’s only 50 years old.

Gwen Stefani and Blake Shelton are shutting down the rumor mill without saying a word … stepping out for a grocery run and looking totally at ease together despite a wave of divorce rumors online.

The two were photographed Tuesday in Los Angeles while shopping at the upscale Italian market, Eataly … grabbing groceries side by side before heading out with smiles that didn’t leave much room for speculation.

Sources close to the couple tell TMZ … the talk is way off base, saying the pair is “completely baffled” by the divorce rumors. Our sources say they don’t even know where the rumors came from, but that they’re complete nonsense and they’re very happy together.