Dracula fucked off to America at the end of the 1700s, leaving the Belmonts to deal with the power vacuum he left in Europe as well as a mysterious prophecy that shit was Going To Go Down at some point.
This Went Poorly
Belmonts dealt with three major vampires in the century that followed - Bluebeard, Springheeled Jack and Jack the Ripper. They'll probably get their own information post.
Bluebeard is the noteworthy one here because in order to deal with him, the Belmont family had to make a deal with the Fair Folk, and traded the firstborn son of each generation to them.
It was a desperate situation okay at least they didn't set London on fire again for this one.
Trevor was born in 1900, had his childhood dedicated to No Seriously Something's Going to Go Down You Need To Be Ready training, because that ~prophecy~ was on the way and we all know that the only things that can ever go wrong are spooky supernatural things and humans never fuck up and
Yeah, turns out that the prophecy was about World War 1 and it just never occured to the Belmonts that it would NOT be vampire bullshit.
(Okay yeah technically WW1 IS vampire bullshit in canon but we're playing fast and loose with canon)
Enlisted in France due to Romania not getting into the war and the family wanting Belmonts involved. Despite being 14.
Originally was trained as French Air Force but then puberty happened and he got too tall and he got shunted into the trenches.
Belmont house was caught in a bombing but he still totally 100% believes this is Dracula's fault
Went to America to get murdered by Dracula. Dracula is busy sulking about his dead wife tho and is not home. Attempted to get murdered by Alucard instead.
Came here to get attacked and is not having a good time right now (because nobody will attack him).
Stabbed Alucard and then got adopted by him.
Also got adopted by the local vampire hunting community of the eastern orthodox church, who are a knitting group of tiny church ladies. They are all his grandma and he loves them all.
May or may not be getting dragged to hell at halloween. Because #fairylife.
1920s AU (aka HIM A FAIRY?????)