toddler having accidents after baby brother born

K so my oldest son will be 3 in November and he has been potty trained for like at least 6 months now with zero accidents. ZERO. Now I have a newborn, he's 3 weeks old and for the past four or five days, my toddler has been pooping his pants every single day and peeing his pants. He also wet his bed one night. Could this have anything to do with his baby brother being born? And what do I do about it? I must admit I am completely clueless because potty training him the first time was so incredibly easy. I literally just put regular undies on him one day and that was that. HELP!!