I have Nimbus from Bluestone and have not had any seedlings from it. I also grow tons of other geraniums some of which do reseed. They way I understand that sometimes nature makes things work in mysterious ways- if you read comments on Plant World seeds some of their supposedly sterile geraniums do produce seeds although in very small numbers...

I was looking up some other garden topic on the net and found a quote in a clematis book, of all things, saying that Geranium 'Nimbus' was definitely NOT sterile. I guess that answers my own question. This agrees with what you said Lindalana about supposed sterile geraniums not being so. That said, I have never had seedlings from 'Rosemoor', another "sterile" one.

Can you show a photo of your plant and a close up of the flower?

Sorry, I don't do photos yet. The quote about 'Nimbus' NOT being sterile was from Gardening with clematis: design & cultivation By Linda Beutler.

My understanding is that most of the so-called "sterile" Geraniums, are only mostly-so, i.e. they are not 100% sterile.