During the final moments of the battle with Morgana and Helios' army, Merlin and Gwen return to the throne room to see their new friend Isolde, dying in the arms of her lover Tristan. Upon witnessing Isolde's death, Arthur realises that he cannot lose Gwen again and forgives her for her crime of 'adultery' with Lancelot. Upon returning to his chambers, he finds Gwen cleaning up. After telling her that he didn't care what she might have done in the past and that he cannot bear to lose her again he proposes to her again, to which she happily accepts. Sometime later, the pair are married and a coronation is held. The doors open to reveal (similar to Morgana's vision) Guinevere walking down the centre of the Throne room with a proud looking Arthur watching her. She then kneels before him. He then crowns her his queen before sharing their first kiss as a royal couple. A chorus of 'Long live the Queen' echoes through the room as Merlin, the knights, Gaius and everybody else watch on happily (The Sword in the Stone).
There were some slight differences between Morgana's vision and the actual crowning of Guinevere, namely Merlin's clothing, Arthur's crown, whether or not Arthur and Guinevere kiss and some of the characters present.
Guinevere is the only Queen of Camelot to be coronated by the King of Camelot and not by Geoffrey of Monmouth. This may be because Guinevere was not born into a noble family. Perhaps, only a King can coronate a commoner, just as a King can bestowe a Lordship or a Knighthood. Conversely, Arthur may have coronated Guinevere himself to show all of Camelot that their union was solid and to express to Guinevere his love for her.
Guinevere has a similar crown to the one Lady Morgana had when she was crowned. The reason for Morgana having the same crown as Gwen may have something to do with her vision of Gwen being crowned Queen. Morgana wearing the crown she saw in her vision of Gwen's coronation may have been Morgana's, possibly subconcious, revenge on Gwen by claiming herself as the 'rightful' one to wear that crown.
Arthur and Gwen's first kiss as the King and Queen of Camelot
'Long Live the Queen!'- King Arthur Pendragon
Arthur helps Gwen to her feet after crowning her Queen
Guinevere, Queen of Camelot
Morgana's vision of Gwen becoming Queen
Merlin and Gwaine
Merlin, Elyan, Gaius and Gwaine watch on proudly
Arthur and Guinevere, the Once and Future King and Queen of Albion