Toddler behaviour

We have a nearly 3 year old and his little life has been turned upside down as we welcomed his new little brother on Monday! He has adjusted really well but over the past couple of days he has been very demanding! “Give me my toy back now daddy!” “Make my lunch now mummy!” This is such unusual behaviour for him! We’ve been telling him off for this and explaining about kind words - please and thank you and praise him when he does this! Is he just put out by new brother or is there more to this as we never had this behaviour before!