Ever heard of Rosemary Lily Evans? No. Well, what if I told you she was Harry Potter's older half sister? Still not ringing a bell? Well she was conceived in her parents fifth year before roughly two months before her parents exams. Lily was going to tell Severus, but their friendship fell apart. But she didn't get rid of the baby, but left her in the care of her parents while she finished school. She named her daughter Rosemary Lily Evans and this is her story.

(August 12th 1980) [age 3 years 7 months] Third Persons POV

It was mid afternoon at the Evans house. Little Rosemary was in her room making her toys fly. Meanwhile downstairs Severus Snape had arrived after being invited by Mr and Mrs Evans for a cup of tea. "We can't thank you enough dear for letting the authorities know about the danger our daughter and James were in. Now they are safe, along with their son" Mrs Evans states.

"I'd do anything to ensure Lily's safety" Snape tells her.

"We know" Mr Evans says. They hear a crash from upstairs. "She's doing it again" he mutters.

"She's only playing" Mrs Evans tells him tiredly.

"Who?" Snape asks them confused. Mr and Mrs Evans share a conflicted look.

"He has the right to know, it was why we invited him here" Mrs Evans tells her husband.

"I still say Lily should of been here for this" Mr Evans states.

"You know why she can't be and she already gave her blessing for him to know" Mrs Evans reminds him. "Come Severus" she says and leads the way to Rosemary's room. Which is Lily's old room. "Rosemary, we're coming in" she says.

"Ok Grandma" she says. Snape frowns in confusion at the child's voice. They enter the room and he is stunned by the sight before him. It was a miniature version of Lily. "Who's that?" Rosemary asks shyly as she clanged to Mrs Evans skirt.

"Take a closer look, you'll know who he is" Mr Evans tells her gently. Nudging her gently towards Severus. Rosemary looks up at Snape with her bright green eyes. She gasps and looks at her grandparents.

"Is he my..." she starts to ask and they nod. "Daddy!" she cheers launching herself at Snape wrapping her arms around his legs. "I knew you'd come one day, mummy promised" she states.

"Explain this" Snape says.

"Lets take this to the living room, Rosemary remain here" Mr Evans says.

"But I want to stay with Daddy" Rosemary says with a pout.

"You'll see him soon" Mrs Evans assures her. "Why don't you draw a picture?" she suggests. Rosemary nodded her head and let go of Snape. She went to her colouring table and started to draw as the adults left.

Once they reached the living room and sat down. Mr and Mrs Evans explained about how Lily got pregnant. How she gave birth of the Christmas Holidays in her sixth year. How they raised Rosemary while Lily completed her schooling. That they have continued to raise her the last year and half while Lily started a life with James.

"But we're old Severus and are very ill" Mr Evans states.

"We had hoped Lily would take Rosemary and raise her along with Harry with James' help. But she said it was time you knew of your daughter. She wishes you to raise her until Lily and her family are safe from you know who" Mrs Evans explains.

"Then what? She takes my daughter from me again?" Snape demands.

"She didn't mean to keep us apart" Rosemary says sadly. Her hair blue. Snape looks at it shocked.

"Rosemary dear, your hair" Mrs Evans states.

"Oh not again" Rosemary whines. She closes her eyes and focuses on her hair turning back to red. It does so. "I'm sorry" she says.

"It's not your fault dear" Mrs Evans assures her.

"She's a metamorphus" Mr Evans tells Snape.

"That doesn't sound right" Mrs Evans tells him.

"Metamorphmagus" Snape tells them.

"That' the word" Mr Evans states.

"She is a witch" Snape says.

"Will you raise me daddy?" Rosemary asks. He looked at her thoughtfully. Before nodding.

(October 31st 1981) [age 4 years 10 months]

Rosemary has lived with Severus for the last 15 months. She wanted to change her last name to Snape. But Severus refused to let her. As Lily gave her the surname Evans and she should honour her mother's wishes. Anyway the Potters are safe, they have a secret keeper who'd never betray them. Severus took Rosemary trick or treating, before putting her to bed.

When he felt his dark mark burn as he was summoned by Voldemort. He summoned a Hogwarts elf to come watch over Rosemary and went to Malfoy Manor. Where he learned that the Potters had been betrayed. They'd be attacked that night after the meeting by Voldemort himself, while he sent he Lestranges and the new recruit Barty Jr after the Longbottoms.

Severus went to warn the order after the meeting after checking on Rosemary. But he was to late, James and Lily died. Yet Harry survived. Dumbledore wished for him to raised somewhere where Lily's blood dwell. That left only two options, Severus' house with him and Rosemary or the Dursleys.

Snape refused to raise James Potter's son, though Rosemary had begged him too. It was the only time he ever said no to his daughter. She ignored him for weeks afterwards. Until he got her a Bengal cat, she named Jade. Though she was still upset with her father, she understood his reasons. She just prayed her Aunt and Uncle took good care of Harry, like Snape has her.

(November 1st 1981) [age 4 years 11 months] Snape's POV

"You asked to see me Professor Dumbledore" I drawl.

"Yes, in light of resent events. I feel like you and Rosemary should be kept close to Hogwarts. And it happens we have a job opening here" he tells me.

"Did Professor Jones quit already?" I ask. Professor Jones got the position I had applied for over the summer. And teaches Defense Against the Dark Arts here.

"No, but Professor Slughorn has chosen to retire" Dumbledore tells me.

"You want me to teach potions?" I ask him.

"Why not? You are a highly skilled Potion maker and have all the qualifications for it. I'm sure given some time, if you're patients you may teach Defense in future. But we need a new Potions Master and head of Slytherin House. You'd suit both rolls and I'd be killing two bird with one stone. As the muggles say" he states.

"But what about my daughter?" I ask him.

"She is a very well mannered child, she may come with you while you teach here. The elves and other professors will help look after her while you are teaching" Dumbledore tells me. I wanted to refuse, but Rosemary deserved more then being stuck in my small dark house at Spinners End until she was 11. So I agreed to be Potions Master, on the condition that no student was to know that she is my daughter.

A/N

Picture above of the cover with Rosemary through the years and her cat Jade.