When Arthur, Merlin and Gwaine got the Cup of Life, they however got caught by Cenred's gaurds who then took the Cup of Life to Morgause and Cenred. Morgause then made Cenred's army immortal using the Cup of Life and she betrayed Cenred and had him killed to gain full control over the immortal army. Uther was soon aware of this when Sir Leon discovered that the army was immortal and he ordered the knights to defend Camelot.
Morgause then used the immortal army to seize control of Camelot and Uther was defeated and captured. As a result of Uther ordering his knights to defend Camelot, many knights were killed as a result while some including Sir Leon were captured. Elyan and Gaius managed to escape the attack and they along with Gwaine hid in the outskirts of Camelot. Uther was then dragged into the throne room where Morgause removed his crown. Morgana then appeared and revealed her true loyalties to Uther and everyone in Camelot while Arthur and Merlin secretly watched. After this Morgana was crowned queen and she used this position to slowly destroy Camelot.
However Morgana's victory only lasted for a week because she was later overthrown by Arthur, his knights and Merlin (The Coming of Arthur).