"The Fate of the Phoenix!"
Lilandra is ready to destroy Jean when Charles challenges Lilandra in a duel of honor. She grants the duel to the X-Men with Jean's life in the balance as each X-Man is allowed to rest and prepare for their part in the duel. The X-Men are teleported to Earth's moon where they face the Imperial Guard for Jean's life as the X-Men split up to try and divide and conquer the Imperial Guard, who are too much for the X-Men to handle. But when it comes down to it, Jean sacrifices herself to save everyone.
Dark Phoenix dies.
*Jean Grey makes the ultimate sacrifice in the heartbreaking climax of the unforgettable Dark Phoenix Saga! Summoned by the alien Shi'ar to answer for the cosmic crimes of the Phoenix, Jean Grey must stand trial - by combat! The X-Men and the Shi'ar Imperial Guard do battle on the moon to decide Jean's fate! But can she keep her dark side under control? Or will the Dark Phoenix rise against her friends? One of the greatest love stories in all of comics - Jean Grey and Scott Summers - ends in tragedy in an issue that shocked X-Men fans and sent ripples through the entire comics industry! It's one of the all-time great Marvel comic books, boldly re-presented in its original form, ads and all! Reprinting X-MEN (1963) #137. *Source: marvel.com