WARNING: The following contains major spoilers for "Fadeout," the Arrow series finale, streaming now on The CW.
When he was transformed into the Spectre during the "Crisis on Infinite Earths" crossover, Oliver Queen used his cosmic powers to reboot all of reality, creating a new Earth-Prime as a result. This version of the planet had a new history, and some pretty considerable differences: Black Lightning and Supergirl were now on this same Earth, John Diggle and Lyla Michaels now had two children instead of one and Star City had become a crime-free metropolis.
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Essentially, Oliver and the seven Paragons remade Earth how they wanted. That is why Star City had been saved. But Oliver didn't just stop there: he also brought back to life plenty of loved ones he had lost over the years. And in the Arrow series finale, we discover these changes have led to an unexpected marriage.
In the series finale, we learn that, in rebooting the universe, Oliver brought back three of the closest people to him: Quentin Lance, his mother Moira Queen and, perhaps most importantly, his best friend Tommy Merlyn. Tommy was a series regular in Season 1. He and Oliver were as close as brothers, and upon learning that Oliver was alive after spending five years away on Lian Yu, Tommy welcomed him back with open arms. However, the situation had become a little complicated, since Tommy had struck up a romance with Laurel Lance, Oliver's girlfriend, before going away.
Now, Season 1 featured plenty of ups and downs in Oliver and Laurel's dysfunctional relationship, and Tommy ended up being caught in the middle of it. Still, he proved his love for Laurel when he saved her life during the Undertaking. Unfortunately, that heroic act cost him his life.
However, in the new history of Earth-Prime, we learn that isn't what happened at all. Tommy never died during the Undertaking, which means he was around for the eight years that followed. And, in that time, he ended up getting married... to Laurel Lance. Clearly, in this version of history, the two were able to patch things up and experience real happiness together. Unfortunately, Laurel still died, presumably at the hands of Damien Darhk, just as it happened in Season 4.
The revelation that Laurel and Tommy were married comes when, at Oliver's funeral, he comes face-to-face with Earth-2 Laurel -- the one that survived the universe's reboot. The two briefly talk, and Tommy is of course taken aback by seeing his wife from an alternate world walk around.
Still, it's nice to know that, had Tommy survived his father's attack on the Glades in Season 1, he would have had his own happy ending with the one woman he truly loved.
Arrow stars Stephen Amell as Oliver Queen, David Ramsey as John Diggle, Rick Gonzalez as Wild Dog, Juliana Harkavy as Black Canary, Katie Cassidy as Black Siren, Katherine McNamara as Mia Smoak, Joseph David-Jones as Connor Hawke and Ben Lewis as William Clayton-Queen.