Toddler behaviour after second baby

I had a second baby two weeks ago, and since then my little boy's behaviour has been unrecognisable. He'll be 4 in March and has always been very well-behaved. We never had to deal with big tantrums, even during the terrible twos or the threenager phase. But now every day is a huge struggle, he says no to everything (to food, to brushing teeth, to having a bath, to coming out of the bath, and so on), he screams at the top of his lungs and cries constantly and it's not possible to console him, he throws things, he hits us, he ignores us when we ask a question (multiple times), he whines and grunts and moans instead of using words, he wakes up many times through the night just screaming and crying. We have been really patient and understanding with him because we acknowledge that this is a huge change for him. We are constantly cuddling him, reassuring him, telling him how much we love him, and we both make sure to spend one-on-one time with him without the baby. He was really excited about becoming a big brother throughout my pregnancy and he's actually wonderful with his sister and eager to help with babycare, which we do involve him in. But his difficult behaviour is really wearing us down and we're having a hard time coping especially given that we have a newborn to look after now too. Has anyone been through something similar? Is this the new normal (😢) or will he go back to his old self at some point? How long will this last?