Judas Repented, Regretted or Felt Remorseful

Then Judas, which had betrayed him, when he saw that he was condemned, repented himself, and brought again the thirty pieces of silver to the chief priests and elders, (Matthew 27:3 KJV)
Now when Judas, who had betrayed him, saw that Jesus had been condemned, he regretted what he had done and returned the thirty silver coins to the chief priests and the elders, (Matthew 27:3 NET)
When Judas, who had betrayed him, saw that Jesus was condemned, he was seized with remorse and returned the thirty pieces of silver to the chief priests and the elders. (Matthew 27:3 NIV)

The Greek word behind remorse/repent/regret, μεταμεληθεὶς, is found 6 times in the New Testament and translated as "repent" in the KJV. Though not the usual Greek word used for repentance, it is not always negative. Basically it seems to indicate changing of the mind about something.
He answered and said, I will not: but afterward he repented, and went. (Matthew 21:29 KJV)
For John came unto you in the way of righteousness, and ye believed him not: but the publicans and the harlots believed him: and ye, when ye had seen it, repented not afterward, that ye might believe him. (Matthew 21:32 KJV)
Then Judas, which had betrayed him, when he saw that he was condemned, repented himself, and brought again the thirty pieces of silver to the chief priests and elders, (Matthew 27:3 KJV)
For though I made you sorry with a letter, I do not repent, though I did repent: for I perceive that the same epistle hath made you sorry, though it were but for a season. (2 Corinthians 7:8 KJV)
(For those priests were made without an oath; but this with an oath by him that said unto him, The Lord sware and will not repent, Thou art a priest for ever after the order of Melchisedec:) (Hebrews 7:21 KJV)

μεταμεληθεὶς
According to Strong, this is the meaning:
Literally: I change one care or interest for another
I change my mind (generally for the better), repent, regret.

You can read more about the correctness of translation this article, 'In Matthew 27:3, did Judas "repent" or "feel remorse"? - Biblical Hermeneutics Stack Exchange'.

For those who use KJV may ask, if repentance was the pre-requisite for salvation, why wasn't Judas saved since he repented?

Repentance in Greek simply means to think differently afterwards; a change of mind. If the repentance is toward God, we shall be saved. Judas repented but not toward God. Whether he changed his mind, repented, regretted or feel remorseful is not important. The important thing was what he did next. He did not seek out Jesus. He went and hanged himself (Matthew 27:5).