Honestly, this one threw me for a loop at first. I kept seeing the title 'Bambi and the Duke' pop up on webnovel sites and thought it might be some obscure historical romance riffing on real nobility. Turns out it's a completely fictional, modern romance novel by author Lynsay Sands—it's part of the 'Argeneau' vampire series, which I didn't even realize until I looked it up. So zero connection to any true story, unless you count the whole 'immortal vampire' thing as historical, I guess.
It's one of those books that takes a familiar trope—the paranormal romance with a rakish aristocrat—and just runs with it in its own universe. The title sounds like it could be a historical drama, but it's pure fantasy-romance escapism. The 'Duke' in question is a centuries-old vampire, and Bambi is, well, a modern woman with an unfortunate name. I think the title's meant to be playful and a bit ironic, not a signal of historical fiction.
So yeah, fully fictional. Sometimes the naming conventions in these paranormal series are deliberately a bit cheeky to stand out in a crowded genre.