The answer
The opinion of the fathers of the church is that he attended the Passover but not the Eucharist.
This is clear from the saying of the Lord Christ about His betrayer "It is one of the twelve, who dips with Me in the dish." (Mark 14:20). The phrase "dips... in the dish" goes along with the Passover but not partaking from the body and blood of the Lord where He broke the bread and gave them, then tasted from the cup and gave them. (1 Cor. 11:23-25).
The Gospel of St. John said "having dipped the bread He gave it to Judas Iscariot... now after the piece of bread, Satan entered him... having received the piece of bread, he then went out immediately. And it was night. " (John 13:26-30).
Clearly, in the Sacrament of Eucharist there is no dipping of bread but this was the Passover.
Furthermore, if Judas did partake of the Body and Blood, then he partook it unworthy not discerning the Lord's Body, and partook judgment to himself (1 Cor. 11:27-29). However, the fathers said that he partook of the Passover only; then went to carry out his crime. The Lord gave His covenant only to the eleven disciples.
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Thrice-Blessed Pope Shenouda III of Blessed Memory