Oh, boy.

An upstate New York mom couldn’t believe her eyes when she gave birth to a record-breaking baby boy last month – a supersized bundle of joy nearly twice the size of an average newborn.

Stunned parents Terrica and Shawn anticipated they would have a hefty newborn but were left in disbelief when their son Shawn Jr. arrived on Jan. 31 at Cayuga Medical Center, weighing a whopping 13 pounds, the largest tot ever born at the Ithaca hospital, the facility announced.