shimano implies it won't ( I believe - but I don't know)

(I'm assuming it's shimano)

i dont think it will - my new DT Swiss 240s hub has a spacer for a 10 speed cassette, which needs to be removed if installing 11 speed.

Pretty sure he'll need a new hub.

The small spacer found on the 10 speed is to take up the difference from the wider 9 speed spacing?

If he's using shimano wheels definitely. Some other wheels, mavic ect, no. You just remove the spacer.

He will most probably need a new freehub body, unless his bike is already got a wheel which is ok for 11 speed and is using a spacer - i.e. a new-ish wheel. 11 Speed is wider than 10speed (10 was actually narrower than 9)
So it all depends on what his wheel is and how old I guess.

All worth it as you can go that much faster with an extra gear. 🙂

Without knowing what wheels he has it is not possible to say 100% yes or no.

Without knowing what wheels he has it is not possible to say 100% yes or no.

This, but AFAIK the only wheels that are '11 speed compatible' out of the box are certain Mavics - which have the spacer on the freehub, plus those from manufacturers like DT bought within the last year. Everything else he'll need a new freehub body.

It's all rather confusing this. It would be good if there was some kind of database somewhere that had all the right info. Is it only Shimano 11 speed cassettes that are too wide? I'm also looking at SRAM...(edit: not that I'm the op or anything)