Before Camelot:

As a refugee, Merlin gained his powers by drinking from the Holy Grail. He decided to use his powers to help others. Eventually, he met and fell in love with Nimue, the sole survivor of her village after it was decimated by Vortigern. Merlin decided to give up his magic and immortality so that he can have a normal life with Nimue; so they could grow old together.

Since it was the Holy Grail that gave him power and immortality, it was the Holy Grail that could take it away. So, he and Nimue set out to find Prometheus’ flame, the only one strong enough to melt the Grail, and forge it into the mighty Excalibur. The plan was to use Excalibur to “cut away” his magic. However, they were beset in their travels by Vortigern, and Nimue had an opportunity to drink from the Grail herself before Merlin used it to make Excalibur. Intoxicated by its power, Nimue waited until Vortigern attacked, faked her death, and then killed him out of revenge, thus becoming the first Dark One. She then broke Excalibur in half so that it could not turn her mortal again. In short, she broke Merlin’s heart, and later, trapped him in a tree.

Many years later, Merlin was able to talk to young Arthur and give him prophesies that included pulling the magical sword, Excalibur, from a stone, and becoming king of the small village of Camelot. When Arthur reached adulthood, he became a knight, found and freed Excalibur, only to discover that it was broken. Camelot had already been nicknamed the “Broken Kingdom” due to its lack of a king, so the fact that Excalibur was broken made Arthur fear that Merlin’s prophecy would not come true.

Arthur did establish himself king, and married his childhood sweetheart, Guinevere. However, he became so obsessed with finding the missing piece of Excalibur (the Dark One dagger), that he could think of nothing else. A neglected Guinevere decided to sneak off and find the dagger once and for all. She thought that if she could give it to Arthur, that he could be happy again. Lancelot knew he couldn’t stop her, and also wanted to see his friend’s suffering and obsession end. So, he accompanied Guinevere on her way. Although they were successful in finding the dagger, they could not bring it back to Arthur. Rumpelstiltskin did, however, make a deal with them. He gave Guinevere some magic dust from Avalon that could make things that are broken appear whole again.

Armed with the magic dust, Guinevere returned to Camelot in hopes to make Excalibur appear whole. Before she could use it though, Arthur confronted her. She decided she wanted him to choose her over the sword and so showed him the dust. Instead of choosing her or losing her, Arthur used the dust of Avalon to “fix” her broken heart and Camelot. After that she was blindly in love with him, and Camelot looked like a huge palace.