Who announces to Octavius and Anthony that Brutus and Cassius have arrived near the camp?

The announcement to Octavius and Antony that Brutus and Cassius have arrived near the camp is made by a character named Messala. He informs them of the impending confrontation, highlighting the tension between the two factions. This news sets the stage for the significant conflict that follows in the play "Julius Caesar" by William Shakespeare.