"I choose to look at it as a great loss. My father's planet, his people-- they were destroyed by a galactic overlord who rampaged his way across the galaxy, destroying worlds and killing those he couldn't enslave. My father was one of a handful of Saiyans to survive, and by the time I was born, there were only two. One of them died from a heart disease, and my father died when the Androids attacked. There was another halfling like me, but the Androids got him, too."

Trunks doesn't elaborate on who that halfling was, but he seems more tore up about that last death than he does the others. He never knew the Vegeta and Goku of his time, but he was very close to Gohan. He was the brother and father figures he never had, the mentor who taught him everything he knew about fighting and being a Saiyan.

Knowing the Gohan from the other timeline somehow doesn't make up for having lost the one from his.