On the Mount of Olives,
Opposite the Temple,
Asked him privately.”
Καὶ καθημένου αὐτοῦ εἰς τὸ ὄρος τῶν Ἐλαιῶν κατέναντι τοῦ ἱεροῦ, ἐπηρώτα αὐτὸν κατ’ ἰδίαν Πέτρος καὶ Ἰάκωβος καὶ Ἰωάνης καὶ Ἀνδρέας
There is something similar in Matthew, chapter 24:3. Rather than unnamed disciples, as in Matthew, Mark explicitly mentioned the big 2 sets of brother apostles, who were speaking privately with Jesus. In Luke, chapter 21:7, there is only the vague “they” speaking with Jesus. Mark said that Jesus was sitting on the Mount of Olives (Καὶ καθημένου αὐτοῦ εἰς τὸ τοῦ ὄρος τῶν Ἐλαιῶν), just east of Jerusalem, where he could see the Jerusalem Temple, since it was opposite them (κατέναντι τοῦ ἱεροῦ). Here, these apostolic leaders, Peter (Πέτρος), James (καὶ Ἰάκωβος), John (καὶ Ἰωάνης), and Andrew (καὶ Ἀνδρέας), questioned Jesus privately (ἐπηρώτα αὐτὸν κατ’ ἰδίαν).