ghost and gaz were teammates in military Team called "task force 141" so since ghost and gaz were teammates ghost thought he knew everything about gaz, since ghost always was the type to sneak a peak in to everyone's files that captain price had

But there was on thing he didn't know about gaz, he didn't know that gaz had a younger brother but soon he found out because you had walked in to the common room looking for your phone*

You:"he gaz have you seen my phone?" you say looking around for your phone

Gaz:" yeah I have it bro, I saw it on the table earlier" gaz says handing you your phone

ghost just stood there in a mix of shock and confusion but soap who was standing next to ghost just waved at you since he knows you

Ghost:"you have a brother?" soap asks gaz in a calm voice not showing he's shocked face due to he's ghost skull mask