A 4-month-old boy who became a social-media sensation when his mom dressed him up as Bernie Sanders died of Sudden Infant Death Syndrome, it was disclosed Thursday.

A photo of Oliver Jack Carter Lomas — in a messy wig, black glasses, a button-down plaid shirt and red tie — went viral after Sanders held the boy in his arms on Feb. 14 in Las Vegas.

Oliver died on Feb. 25, his mother, Souxsie Lomas, announced on Facebook.

“I love you dearly, I love you most. I love you with all my heart and soul,” she wrote.

The Sanders campaign tweeted: “Oliver will always be in our hearts & be remembered as Bernie Baby who brought us joy during our trips to Las Vegas.”

He will be buried Monday in Hollywood Hills, Calif.