Can you point me to where this third Elijah is referenced in Scripture please?
Matthew 17:11-12 is one place, in my opinion. Also, many theologians believe that signs given in Scripture for the coming of the Messiah (first coming of Jesus) actually apply most times to the second coming as well. So an 'Elijah" would be expected for each of the two comings.
Matthew 17:11-12:
*
He said in reply, “Elijah will indeed come and restore all things;
but I tell you that Elijah has already come, and they did not recognize him but did to him whatever they pleased. So also will the Son of Man suffer at their hands.”*
Malachi is another place, for its speaks of an Elijah who will come before the great and terrible Day of the Lord (ie the Last Day):
Malachi 3:19-24 of NAB version of Bible:
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For lo, the day is coming, blazing like an oven, when all the proud and all evildoers will be stubble, And the day that is coming will set them on fire, leaving them neither root nor branch, says the LORD of hosts.
But for you who fear my name, there will arise the sun of justice with its healing rays; And you will gambol like calves out of the stall
and tread down the wicked; They will become ashes under the soles of your feet, on the day I take action, says the LORD of hosts.
Remember the law of Moses my servant, which I enjoined him on Horeb, The statutes and ordinances for all Israel.
Lo, I will send you Elijah, the prophet, Before the day of the LORD comes, the great and
terrible day,
To turn the hearts of the fathers to their children, and the hearts of the children to their fathers, Lest I come and strike the land with doom. Lo, I will send you Elijah, the prophet, Before the day of the LORD comes, the great and terrible day.*
Interesting that in speaking to Saint Faustina about the Second Coming, Our Lady also used the word ‘terrible’ for that day:
*You have to speak to the world about His great mercy and prepare the world for the Second Coming of Him who will come, not as a merciful Savior, but as a just Judge.
Oh how terrible is that day! Determined is the day of justice, the day of divine wrath. The angels tremble before it. Speak to souls about this great mercy while it is still the time for granting mercy.
- (Diary 635) Our Lady speaking to Saint Faustina
ewtn.com/devotionals/mercy/coming.htm
Remember it is not actually Elijah, but somebody in the spirit and power of Elijah - the actual Elijah is a type for both John the Baptist and this other “Elijah” type who comes at the end.
God bless you.