The answer to WHO Rosalina's brother is.

Chapter Two: The Day That Life Changed For The Worst After a few minutes went buy of Mario emptily staring what seemed to be through Luigi, Peach attempted to break the silence. She took a deep breath and said “Hello Mario, how have you been?”. Mario looked past Luigi and at Peach. He staired at Peach for a long while and after a bit Mario finally cleared his throat and said in a clear American accent “So Lu, you stole my princess and my happy ending. Are you happy with yourself?” He took his eyes off of Peach and began to stair daggers at Luigi. It was unsettling how Mario's hadn't blinked once. Luigi gained enough courage to say “What do you mean Bro?” Luigi positioned himself in-between Peach and Mario. Mario pushed Luigi and said "You heard me Lu. The question is what's stopping me from taking her back? Mario began to barge in and approached Peach. Mario lifted his hand up to tuck a strand of Peach's golden hair behind her ear. Luigi put his hand out to stop Mario and protect his wife. Mario grew inraged, Luigi had never seen his brother this angry before. Luigi tried to place his hand on Mario's shoulder, but Mario grasped onto his hammer. Mario began to swing it at Luigi missing at first. Luigi demanded Mario stop, but Peach got in-between them and was hit in the crossfire. Luigi Jr had gotten out of bed because he had heard unusual noise. Luigi Jr headed downstairs but as he reached the bottom he heard the loud thump. He ran to the front of the castle and hid behind the wall trying to see what had happened, and as he peered into the room to his horror he saw his mother lying lifelessly on the ground as his father ran to her trying to wake her up. Tears started to form in Luigi Jr's eyes as he realized what had just happened and that his mother was no longer alive. He wanted to run but it felt like he was frozen. The only warmth on his body was the consistent stream of tears that now made his sight blurry. Luigi Jr glanced down to see a red cap like the one his father had given him, the red cap had an M on it instead of an L. Could this be his uncle Mario's hat? His father loved to tell them stories of Uncle Mario. As he watched the red cap a white gloved hand reached down to grab it. Luigi Jr regained control and his himself against the wall so to not be seen. Luigi Jr heard his father crying over his mother and he saw him softly holding her in his arms. Luigi Jr walked upstairs trembling and entered his sister's room. He called out to her, his voice trembling more than his hands as he tried to break the news to her. Rosalina sat up in her bed trying to wipe the sleep out of her eyes. What her younger brother was saying surly couldn't be real he must have had another bad dream. She remembered he had been having a lot of those lately. As she walked downstairs with him to show him it was just a dream she too was sent onto a hurdling shock as she stared at her mothers cold lifeless body. In the morning they had a funeral for Peach. The entire kingdom was sent into depression as they watched their beloved Queen being buried. Rosalina took the funeral and loss of her mother the hardest. She could often be seen walking up the hill to the tree where her mother had been buried. Luigi tried to follow her every once in awhile, but it didn't fix his new nightmares. He couldn't get the red cap out of his dreams. He hurt so bad and he didn't know how to fix it. Whenever he got hurt before he would just run to his mother and she would make it better, but now he was hurting so badly and his mother couldn't comfort him.