The unofficial mascot for the Bernie Sanders campaign, and a viral sensation, Oliver Jack Carter Lomas-Davis aka the "Bernie baby," has suddenly died, his mother posted on social media.

Oliver, who was almost four months old, died on Feb. 25 due to SIDS (Sudden Infant Death Syndrome), according to his memorial page.

"Oliver's mother, aunt, and family are mourning the tragic and surprising loss of this incredible baby boy," the memorial page read.

Susan Lomas (L) of Nevada holds her 3-month-old son Oliver Lomas, dressed as Democratic presidential candidate Sen. Bernie Sanders (D-VT), during his campaign rally at Bonanza High School on February 14, 2016 in Las Vegas. Ethan Miller/Getty Images

According to the CDC, about 3,500 infants die suddenly and unexpectedly (SUID) each year in the United States. The causes of death in many of these children can't be explained, and most occur while the infant is sleeping.

Get Breaking News Delivered to Your Inbox

Oliver's mother, Susan Lomas, posted about Oliver's death on both Facebook and Twitter.

"Oliver Jack Carter Lomas... I love you dearly, I love you most. I love you with all my heart and soul. I know that God will keep you near since God and truth are here," she wrote on Facebook.

Dressed up as U.S. Democratic presidential candidate Bernie Sanders, Oliver became a huge hit after a campaign rally in Las Vegas, Nevada, on Feb. 14.

And the resemblance to Sanders was uncanny.

Sporting Sanders' notorious wiry white hair, little Oliver wore black thick rimmed glasses, a tie, and a large Bernie Sanders sticker on his shirt. He was an instant hit, labeled the "Bernie baby."

Even Bernie was a fan of the little guy.

When word of Oliver's death hit Twitter, Bernie supporters began expressing their grief and sadness in droves.

Donations also began to pour in on a GoFundMe page setup by Oliver's family.

By mid-afternoon, more than $17,000 had been donated. The page says the funds will go towards the wake, funeral, and burial expenses, as well as any counseling the family may need.

Oliver will be laid to rest on Tuesday, March 8, in Hollywood Hills, California.