That’ll be Natura’s Star. That’s the epic weapon that was available to purchase while doing the kingdom quest. It was not from an event.
It should have been available in the Soulforge in Nexus weeks, see Natura's Star not in Soulforge.
Don’t spend cash on it. It’ll come round in the Soulforge eventually, even if it isn’t fixed for next week (the last Nexus week for a while).