Buffy the Vampire Slayer (1997)

S6E16 Hell's Bells

As Anya and Xander prepare to tie the knot, their special day takes an unexpected turn when an unexpected guest arrives—an individual insisting he is Xander's future self. His sudden appearance sends shockwaves through the ceremony, causing chaos and uncertainty as the couple confronts the implications of this bizarre revelation. Will they be able to navigate the turmoil and make it down the aisle, or will this twist derail their happily ever after?