Assumedly, you're here for one of two reasons: 1) You've seen Last Christmas and want to compare how early in the movie you figured out its big twist. Or 2) You haven’t seen Last Christmas but have turned to me, dear reader, to spoil you, to see whether the twist is exactly what you guessed it was or gauge if it's wackadoodle enough that finding out what the twist is actually makes you want to see the movie more.
On the latter, this is not some Anne Hathaway-is-a-video-game-character, Serenity-level reveal. It's less "WHAT" and more "aww, yeah, that's what I thought."
First, the premise, for those of you who've not seen the Paul Feig-directed, Emma Thompson-penned holiday romantic (kind of?)-comedy (sort of!): Kate (Emilia Clarke) works as a sales clerk at a year-round Christmas shoppe in London, having officially given up on her dream of becoming a singer. Until, that is, she meets an enigmatic gentleman, Tom (Henry Golding), who might just reignite that spark in her.
Many of you probably guessed the twist from the trailer. Or you at least knew something had to be up, whether it be some sort of Christmas miracle (like that one Will Smith-Keira Knightley movie) or something supernatural, akin to the ghosts of Christmas whenever.
The ghost/guardian angel theories gets a lead out the gate. Watching maybe the second scene Tom is in, I whispered to my friend, "He's not really there, huh." Golding is twisting and swerving out of the way of background extras and lampposts -- seemingly to avoid any interactions with the world at large that would, ahem, give up the ghost.
All the while, Kate vaguely discusses how she "nearly died" the year prior and, as a result of her being "really sick," she now has a scar down her chest. Maybe midway through the movie, it's revealed she had a heart transplant. At this point, my friend -- who, I'm sorry to this man, never predicts twists early on -- leaned over and said, "Is he the one who gave her her heart?"
Twenty or so minutes later, the movie confirms: Yes, Tom did, indeed, die and it was his ticker that was transplanted into Kate. Get it? Because of the titular George Michael song? "Last Christmas, I gave you my heart / The very next day, you gave it away..." It's both a very literal take on the first bit and kind of symbolic on the back half. (After receiving a new heart, Kate stops truly living.)
So you were (probably) right: Henry Golding is essentially both a ghost and guardian angel. The movie montages through all their scenes together to show that Kate had been talking to herself, ice skating by herself, getting changed in an alleyway without anyone providing cover. (I have a few questions about the logistics of some of their scenes together but the gist is there.) But now that his heart is inside her, a piece of him will always be with her. Literally and in a more sentimental manner. And that's the twist.
In some ways, it's basically the same twist as Vice. Happy holidays!