CoA- a question about nationality

I'm filling out the CoA form (permission to marry). It asks for my fiance's nationality and how long he's been living in the UK.
My fiance came to England for the first time over three years ago from South Africa. Besides his South African passport, he also has a British passport (through ancesteral ties). So, for nationality can I put down he's British since he's got a british passport?
Sorry if this seems a daft question, just want to get it right!

Yes, he can! It seems like he is British by descent.

Thanks Docterror