Somewhat lighthearted, but I'd also appreciate advice on how to deal with the sudden onset of "Kevinish" behaviour!
DS (12) started puberty in early summer (visibly at least) and has morphed into a completely different being from a year ago. He used to be laid-back and generally a nice child to be around - his teachers specifically mentioned his kindness towards other children if someone was hurt or upset. He might still be nice at school...but he's being horrible at home!
Everything is a battle unless it's something he really wants to do; he's been verbally unkind to me (later apologises), has to be nagged to shower, tidy up, do his schoolwork (although he's fine once he gets going) and has generally turned into Kevin. 
How do I handle this? DD(15) is argumentative sometimes, but has never been as stubborn as him, he's fighting everything. I'm just blindsided by the metamorphosis!