Iron Man: Legacy of Doom (2008 series) #4

In Scotland, the sky has torn open and a grisly creature composed entirely of eyeballs steps through to face Iron Man and Doctor Doom. Together those two antagonists cannot harm the monster which sucks the souls from the unprotected. The creature heads for the nearest city; by combining their new magic powers, Shellhead and Doom manage to tear a hole in the ground for the monster to fall through. During their respite, Doom reveals that he had borrowed a magic book from this monster and not returned it. When the monster swore vengeance on all his subjects, Doom went through the complicated deal with Mephisto and Morgana Le Fay to obtain Excalibur and its scabbard, together the only way to defeat the monster. The monster returns from the pit, and Doom realizes that from his time as “Emperor Doom” everyone on Earth is technically his subject—and doomed. Merlin then reappears, telling them that Excalibur must be put into its scabbard to become the necessary superweapon—which means Shellhead must be impaled on the sword. They try—and it doesn't work. Turns out it is because Tony doesn't believe in magic; once he can open his mind to the possibility of magic (which he has seen thousands of times) the sword plunging into his chest fires a blast of energy which causes the eye-creature to melt. When all is done, Iron Man and Doctor Doom are back to normal, with Merlin in possession of both sword and scabbard, intending to return it to the Lady of the Lake. The wizard erases the memory of the events from all witnesses, including Shellhead and Doom, and they all part....

Now that Tony has recovered these memories from the computer chip, he immediately flies to England, purchases the land surrounding the reputed lake where the Lady has Excalibur, and orders it covered over with a shopping mall...which is where we find it in IRON MAN 249-250.