Hank Pym
Tigra's physiology is more feline than human. When she became pregnant via the Skrull pretending to be Hank Pym, she carried the baby to term in two months, producing a single Cat Person son named William after her late husband. William does not have any traces of Skrull DNA as the Skrull pretending to be Hank Pym imitated him down to a cellular level; thus, genetically, William is Hank Pym's son. William matures more quickly than a human baby would.