A.T. Robertson Commentary Mark 15:39

"And when the centurion, who stood by over against him, saw that he so gave up the ghost, he said, Truly this man was the Son of God." — Mark 15:39 (ASV)

The centurion (ο κεντυριων). A Latin word (centurio) used also in verse 44 and here only in the N.T.

Which stood by over against him (ο παρεστηκως εξ εναντιας αυτου). This description alone in Mark, picturing the centurion "watching Jesus" (Matthew 27:54).

So (ουτως). With the darkness and the earthquake. See on Mt 27:54 for discussion of "the Son of God," more probably "a Son of God."