@Mumoffootieboys, there is a book called Divas and Doorslammers by Charlie Taylor, in which he says that teenagers’ brains are actually rewiring during adolescence - structural change is happening - and during this rewiring they can and do lose certain abilities - impulse control, temper control, empathy, sense of proportion (and ability to realise they aren’t the centre of the universe). This is why they seem to change so completely from the child they were before.
He describes it as being akin to temporary brain damage - but it IS temporary, and most, if not all, of these abilities come back once the rewiring finishes.
Ds3 was particularly bad during the teenage years - lots of lost temper, grumpiness, taciturnity, shouting and rudeness - I honestly wasn’t sure he’d make it out of the teenage years without ending up under the patio - but we did both make it, and he is now a pleasant young man - still quiet, but happy to have a conversation even with his aged mum, thoughtful, hard working and well able to control his temper.
I would offer to send you my copy of the book, but I already sent it to a friend who was going through the same thing with her teenager.
Rest assured - your lovely boy is still in there, and will come back.