Book for an about-to-be-nine y.o. boy about his body?

[Flanelle]

Suggestions welcomed. He's a quite good reader and ready for something additional to parent chat to help him think about his sexuality and relationships etc.

DD (9.5) has the 'girl' version of What's Happening to me? which is good (though I haven't seen the boy version so don't know if its equally good). Its about puberty but also sex, relationships etc.

We also got her on the recommendation of various MNers Lets Talk about Sex which I think is a little old for her yet but will be perfect in a year or so.

Thanks Takver for book suggestion and link too - very useful!