Tutankhaten ascended to the throne at 9 years old. There is some debate about who his immediate predecessor was, either Akhenaten or Smenkhkare.
What is certain was that under Tutankhamun the Amarna period came to an end. During his reign the royal court left Akhetaten and returned to Thebes. At this time the Aten reverted to its traditional place in Egyptian mythology and the state gods were restored.
Tutankhamun must have also removed some Akhetaten burials and transported them to Thebes. If there was an immediate backlash against the Amarna heresy it is difficult to see how he could have achieved this without high level help, and the person best placed to carry out the task would have been Ay, who is often given as a candidate for Tutankhamun's murderer. Some of the removed objects, including at least one mummy, ended up in KV55 in the Valley of the Kings.
Given the succession from Tutankhamun to Ay, it looks likely that Ay was chosen for this role. The real destruction of the Amarna legacy, including the usurping of Tutankhamun and Ay's monuments did not start until the reign of Horemheb. Perhaps here we have a better candidate for the architect of the destruction that followed the death of Akhenaten and the return to Thebes. In subsequent king lists Horemheb is given as the successor to Amenhotep III missing out the Amarna bloodline altogether. This was a revision of history perhaps intended to downplay his own position as one of the Amarna Periods most influential figures.