Their friends and family (with the exception of Draco, though he never said anything) thought they lived in separate rooms above his shop (located in Vertick Alley, Diagon Alley's countryside cousin). When there were visitors, Hermione made her room look used, rumpled the bedding and left out a book or teacup, and Severus tidied his side.

They'd had a plan. She had half a year left before her apprenticeship was completed, and then they could begin the slow public dance of courtship. She'd go into research, but she'd still live above his shop. She'd confide in her friends (preferably in public spaces where it could be overheard) that she would miss him if she moved out. She would be seen in her presence at the various galas they were all invited to following the war, and he would not appear to be in pain. Within six months, they could've sold the idea of their relationship to the papers; the Guild would do a cursory examination of her apprenticeship and find nothing (because they were both very good at paperwork, even when they were distracted). They could be married in a Wizarding ceremony by the following Christmas.

Instead, some clever charms work hid her growing pregnancy, and the looming end of her apprenticeship excused her absence among her friends. George Weasley was the only one to stumble upon the secret, and Severus made him swear a wand oath not to tell.

Simon (because they liked the name) Wendell (for her father) George (because he'd become a close friend, wand oath and all) Prince (for Severus's mother) Snape was born eight months after her apprenticeship concluded.

So began the ruse.