I used to watch Lily's son sometimes. At night, when Vernon was snoring soundly, and Dudley was long tucked up in bed. I would creep downstairs and stare through the grate at the boy. I hated him, hated him for being so… so like Lily.

I tried to help Dudley. I didn't want him to feel like me, the second child, the one that wasn't worth a damn. I wanted Dudley to be loved, to be more important than my nephew. Magic didn't make you a better person, after all. I wanted them to have an equal chance. But sometimes I think I went a bit far in trying to even out the ground.

I remembered when I was just a girl, and then baby Lily was born. And all the grown ups wouldn't stop talking about Lily's beautiful eyes, so green where mine were so pale. And I'd felt so jealous, that it was little Lily getting all the attention. But then I'd screamed at Mum and she sat me down and read me Enid Blyton's Mallory Towers every night that week. And I'd been so pleased that Mum was reading to me every night, just a little time without Lily. And at the end of the story, when Sally learnt about sisters, I felt my jealousy evaporate and felt instead joy. Of course Lily would love me. I would be the best big sister ever.

'TUNEY! TUNEEEEY.'

Lily was yelling for me. Not mum or dad, because sometimes a big sister was the best person to go to when you were hurt. Sometimes a big sister was the only one who could make it feel better.

'Hey Lily, it's OK, I'm here now.'

And she flings her arms around me, and I talk to her, murmur soothing words to make the pain go away.

Sometimes I knew that her son was crying too. But I couldn't bring myself to comfort him.

'Hey Tuney'

'Yeah'

'I was wondering, I saw on a movie these two sisters who had a secret handshake, can we have a secret handshake?'

'Yeah, sure Lil.'

… Clap, punch, shake, spin, clap …

Dudley wasn't going to have a brother, I'd make sure of that. Siblings just run out on you when you need them most. And I wasn't going to forget my child, make the same mistakes my parents had done. I hoped the boy wouldn't get the letter. Then maybe I could give him a hug and forget the last 10 years.

Maybe if I only gave him a minimum food, he wouldn't have any excess energy for magic. Maybe if I didn't give him any love, he wouldn't be able to perform spells.

But when he got the letter, I wasn't shocked. I had already experienced someone normal, someone part of my life, just going away.

I hoped he wouldn't come back.

When Lily came back from school she would smile and chatter and laugh all the time. She would show my parents her books and photos. Her and her friends, having the time of their lives without me. And all the neighbours would sigh and say how great it was she was back. Lovely Lily.

But my nephew wasn't like that. He looked fatter, and definitely happier than usual, but he seemed to get headaches. It got better as the weeks went on, but it was like he was recovering from a rather bad accident.

And no letters. Lily had had owls flying in and out her window everyday. Not a single letter for him. Strange. I made him work hard. Don't want Dudley thinking that magical people don't have to work too. And suddenly I couldn't bear to let him go. Lock him up, like I should have locked her up. Stay here with me. Listen sometimes, ear pressed to the door. He paced a lot.

And the year after. Lily was much the same, a bit older. Not such a baby. He looked older too. Quite a lot older. And that weird thing with Vernon's sister. Blowing her up. If Lily had blown her up it would have been funny. Little Lily looses control, fixed in a flash. But not so funny when it happened to her.

I listened outside his door on the night of his birthday. Scratching of a quill before the window opens. I here ripping of paper, stifled laughter. It reminds me of Lily's birthdays. She got presents through the window at midnight too. And my present wasn't as good as the magical ones.

But after Dudley had finished year 9, something seemed to be alight inside the boy. He flickered endlessly between a sort of dull depression, and a wondrous happiness. I knew he was getting owls too. Probably food. Let Dudley have the bigger quarter, his cousin could live on magic. And I noticed that we couldn't control him anymore. He didn't seem to care what we thought. He has his Godfather now.

And then those people come to fetch him. A family. Like he didn't already have one. But to my nephew we're not parents, and Dudley was never a brother. We're just jailers who lock him up in cupboards. Those red heads blow up our living room. And almost kill my Dudley. But they don't seem to care about us, just Lily's son. Like he's something more special than us, because he can do magic.

The year after that was a much bigger change. Not just your normal sudden growth spurt, the sort of changes you'd expect in your 14-year-old nephew you hadn't seen for a year. Haunted eyes. Dark with pain and anger and an endless tiredness. He wore a t-shirt one day and I saw a long, thin, raw scar on his arm. I wonder why they haven't healed it.

'Boy, pass the butter,' says my husband. I look up, to see my nephew sitting at the table. It's a rare occurrence these days. In fact probably the first time this holiday. He doesn't respond, sits, contemplating his piece of toast.

'I said pass the butter.' Vernon is getting angry now, the ugly vein in his temple beginning to throb. I stare at the boy in front of me, totally oblivious. He flinches.

'ARE YOU DEAF,' he roars. My nephew looks up, slightly bemused. Passes Vernon the butter, then walks out the room like nothing happened. He doesn't eat with us again.

I listened at his door at night. I used to listen at Lily's, hear her laughing quietly at a letter from a friend. Or the steady scratching of a quill on parchment. But I'd listen at his door and hear moaning and barely stifled screams. Then the flick of a switch to mark another sleepless night. Strange behaviour too. Watching the news. Vernon said that he was a freak, strange behaviour was a mark of his kind. Didn't tell him Lily had never bothered with the news at his age either.

And then he came back with my boy in tow. My boy, ill and trembling, reduced to a wreck. And my nephew was supporting him on his arm. We blamed him, Vernon, Dudley and I. Had he let all that anger and pain behind his eyes flow out and hurt our Dudley, just like he'd hurt Marge in anger? And then I had eyes only for my son. Dementors, said the boy.

I'm listening outside Lily's door again. I don't like coming in anymore, seeing the spell books and robes and parchment makes it real, but it's still comforting to hear her voice. She's got that damn awful boy staying here. Come to experience muggle life apparently.

'James, I was wondering, what are dementors actually like? I mean I've read about them but…'

'Yeah. You've never been near one.' The boy wasn't laughing, for once. 'Imagine your mind as a jumble of thoughts and memories Lily, and some are happy, but some are sad. The dementors take away every single happy thought. Only the ragged edges of your worst memories are left, with nothing to take the pain away. It's like…life isn't worth living anymore.'

My mouth is a little round O of astonishment, and I can almost hear that Lily's is the same.

I think of dementors attacking my son. Dementors, in my so carefully ordered life. And then he mentions Voldemort, and another shiver goes through me. I had hated Lily, for being so bright and perfect, hated her, but never wanted her dead. Never wanted her murdered. I remembered that last summer, when her smiles seemed to be a bit more forced, when she had cast charms outside our door. When she had leaned heavily on James' arm, and they'd exchanged looks full of meaning. I stole one of her newspapers once. Death and destruction on every damn page.

I look at my nephew, and he catches my eye, and seems to see something more than usual. Like he suddenly remembers that I am his Aunt by blood, his mother's sister, not just Petunia Dursley. Vernon is shouting now, but I am too shocked to listen. Memories are coming rushing towards me, things I've tried to hide now for so many years.

And then that letter comes.

'Remember my last, Petunia.'

And I remember. While the boy stays, he lives. If he goes he…

'The boy - the boy will have to stay, Vernon.' For Lily, who I never wanted to die.

The year after that, he is changed again. His shoulders are hunched, and there are, to my horror, lines on his face. 15, I think, 15. He looks like he has lost someone who was important to him. He ignores us now. All those other years he was angry, angry at having to return. And I was pleased in a way, that I still had some control over his life, like I'd never had over Lily's.

But now he seemed to have simply accepted that he must be here. He wasn't happy about it, but it seemed to have sunk to the bottom on his list of things- to-be-worried-about. I went to his door at night again. He was muttering still, but different words. 'Sirius, Sirius, Sirius' he would say. And sometimes, more disturbingly, 'my fault'. Not that he slept often.

And then that man had turned up at our door, sat down in our house and talked to my nephew like he would to a colleague.

'His Godfather's dead?' said my husband. I glanced at the boy. Although he gave no obvious sign of pain, his eyes were shut for a split second longer than usual when he blinked next. Lily had been like that, never wanting to show when she was hurt.

They had a conversation about names and places of which I had not heard, but called to me like half forgotten memories. I saw my nephew spring to his feet at one name. Hot temper. Even I, who knew so little about the boy who had lived under my roof for so many years, knew that. And then he brought that disgusting, dirty little creature into my house. All those years of scrubbing the place, scouring out the ugly thoughts and bad memories, to have magic appear in its most base form.

He tells me that the boy will come of age next year, but that is wrong, and I say as much. But of course, he even has to be a man before Dudley. Fed up of someone younger always outshining me at everything, I'd cleared out before Lily came of age, so I wouldn't know that their kind are adults younger than ours. I wonder vaguely if Dudley will be jealous.

And then that man reveals the truth. That in trying to protect my son, I have neglected my nephew. That in trying to overcome the jealousy ingrained in me years ago, I have ignored the one thing left of my sister. The truth that I have been hiding to my consciousness was bared openly, before me. That jealousy has made me a cruel person.

I dread the last year. He has changed again. This time his eyes aren't sorrowful, but awfully hard. Like there is nothing left of him but a soldier. I am worried. I hate him, but I don't want him to die. He doesn't avoid us this time, doesn't hide away. He takes us in his stride. Telling us what to do.

Dudley says goodbye to him. I am proud of him. He doesn't allow his envy to eat away at him, to fester. He accepts Harry for what he is. That's why I cry and fuss. Because Dudley won, where I could never win.