Northern could have sworn he was already following the pathway and was sure that the murals were the last journey of the Chaos Prince.
Although he didn't quite see the end, he assumed that whatever end the Chaos Prince met was at that temple, escorted by those maidens.
The reason for that assumption was because that was where the Vestige of the Chaos Prince was found.
Moreover, an entire statue of him was built in the place.
'I thought that was the last timeline… was I wrong?'
The Tower didn't exclusively record anything pertaining to the Chaos Prince's death.
It just mentioned his magnificent deed of seeking out the Void. After the Chaos Prince merged with Void, his downfall started.
Fagnur had written that the Chaos Prince began to change.
But nothing was there about his death and what led to it.