My LO becomes aggressive

Hello, mamshies. I have a son turning 3yo soon who is capable of breaking his toys whenever he is angry. I wonder why he behaves like that. We are all loving towards him. Whenever he commits mistake, we as parents gently tell him the what is wrong and he gently responds, "I'm sorry, Nanay/Tatay. I won't do it again." But there are times when any of his cousins goes to our house and tries to play with him, he will pull right away whatever toy the cousin is holding...either he throws it or breaks it in front of his playmates, especially if an adult tries to correct his behavior of suddenly pulling the toys. It is so alarming because he wasn't like that before, not until he turned 2yo (2 1/2, to be specific). If i am told about what he does to other kids, I would directly ask my son what he did on that partcular day. He would gently admit to me that he fought his cousin. His reasons were THEY WERE: 1) Not playing with him (maybe they are scared) 2) Getting his toys (maybe he thought they were taking his toys away) And sometimes he reasons out that he was just angry. Anyone who experiences this? I asked hia pedia but she told me to observe again his behavior. Thanks a lot! #pleasehelp #1stimemom #advicepls