A/N: Hello all, here with my first Once Upon a Time/Harry Potter Crossover, and my very first time writing in the Marauders' era!
Now this came about as a backstory for a roleplay that I am partaking in which involves the premise that Regina attended Hogwarts. This is going to be a very loose interpretation of Once Upon a Time canon, but takes place in such a way that seasons 1-6 exist as they are for the most part minus certain Regina backstory details. Harry Potter is playing very loosely with canon, but I hope that doesn't deter anyone.

This story will take place both in the present and in the past, and the present takes place before Harry is born.

As far as Once Upon a Time goes, this begins during the flashback portion of Is This Henry Mills? 7x20.

I do not own Once Upon a Time, that belongs to ABC and rightful owners. I do not own Harry Potter that belongs to JK Rowling, the queen. I'm just playing in the sandbox.


Prologue

Regina Mills had received several letters in her life, but only three by owl. The great bird was not one that she was particularly pleased to see perched on her desk at this time of the day, especially since in a matter of hours, she and her son were due at Granny's to celebrate his graduation. At the same time, that the owl made its presence known with a soft but insistent hoo, Regina heard the phone ring. An excuse to pretend this isn't happening. Regina sighs in relief and is just about to reach for it when she hears her son call:

"Got it Mom!"

Well, Henry is eighteen now, more than capable of answering a phone call. Drat.

Hooo! The bird lunged forth and nipped Regina's hand insistently holding out its leg.

"Yes, yes I see you." Regina muttered. She bends down and unties the message from the owl's leg. "Thank you." Regina takes the envelope in her hand. She recognizes the heaviness of the parchment, can almost feel the ink of a quill's stroke staining her fingers. As is usual with this type of correspondence, it is as if the letter writer knows much too much.

Miss Regina Mills

Storybrooke Maine

The Largest House on Mifflin Street

The Corner Office

Regina opens the letter and takes note of the length, reasonable considering the amount of time that has passed. A photograph slides out as well, a group photo, quite a certain group.

Hello Gina,

Have you been well? I certainly hope so. It took me quite a while to find your address. Even Professor Dumbledore had to reach out to a few more contacts. I hope I've found the right one. Anyway, by all appearances, it seems as though you've left this all behind you in America now. I'm terribly sorry to have to drag you back in. Of course, it's entirely up to you in the end. Since you left Hogwarts, I'm afraid things have gotten ever so much worse. You do remember our talk back then: fighting back? Well, the Order's been established. I'm afraid I can't say much more than that. We could use all of the help we could get. Will you help us? Please do let me know. Chauncey knows where to go, don't worry about an address.

Cheers

Your Friend Always,

L.E.P.

Regina is taken aback hearing from Lily Evans, well Potter now she supposes. There's only one she knows from back then with the initial P. She conjures herself an inkwell and parchment and writes back.


When she returns to the living room, she sees a note from Henry on the coffee table.

This is the admissions essay I wanted to send but couldn't. It's called Once Upon a Time, and it's the story of us.

Regina feels immense pride reading Henry's essay. She can almost forget the letter she wrote. Almost, but not quite. This is a part of her life she'd wanted to keep separate. But now, well she supposes her story is not quite finished despite the end of Henry's book.

"Mom," Henry comes downstairs dressed for the party. It takes Regina a moment to bring her focus back. "I think...I made a decision."