A cute-as-a-button cheerful baby boy who sported a gray wig and horn-rimmed glasses at a Bernie Sanders' campaign rally to become an instant internet sensation has tragically died of Sudden Infant Death Syndrome at the age of four months.

Known as "Bernie Baby" for his uncanny resemblance to the Democratic presidential candidate once he donned his dress-up garb, little Oliver Jack Carter Lomas-Davis died in his sleep at home, said his mother, Susan Lomas

"Oliver Jack Carter Lomas-Davis was an adorable infant who brought smiles to not only his family, but to millions online," said the family on the baby's memorial page. "Oliver's mother, aunt and family are mourning the tragic and surprising loss of this incredible baby boy."

His mom posted: "Oliver Jack Carter Lomas, I love you dearly, I love you most. I love you with all my heart and soul."

The baby's aunt told Associated Press that Oliver was "happy, joyful and full of love, and he shared that with everyone he came into contact with. He was extremely healthy and was tragically taken too early by SIDS."

Oliver became a huge hit when he showed up with his mom at a Sanders campaign rally in Las Vegas in mid-February. Besides the gray wig and glasses, Oliver wore a tie and a large Bernie Sanders sticker on his plaid shirt. He completely captivated his elder look-alike.

The Twitterverse responded in grief at the news. "So sorry about your loss," tweeted Veterans for Bernie. "Oliver will always be in our hearts and be remembered as Bernie Baby who brought us joy during our trips to Las Vegas," tweeted the Bernie Sanders Brigade.

Close to 3,500 infants die of SIDS every year in the US. The exact causes of deaths in many of the cases can't be determined, and most occur while an infant is sleeping.

Oliver's family is raising money to help cover burial expenses and counselling. He'll be buried in Los Angeles.