Jonna, Hi, I don't think it is the Grand Duke. The flowers on the Duke get flowers as big as 4-5 cm. Otherwise this certainly fits much of its discription. Do you have the little booklet from Top Tropicals called Jasminujm Sambac Absolute Flower . I got mine at www.TopTropicals.com. They have pictures of many of the Jasmin Sambac and in there they mention how difficult it is to figure out some of the plants growing.
The Duke I had looks like this and the plant looks like a bush with straight vertical branches and is very slow growing.
But, they are single flowers and large like gardenias. The Mysore Mulli could be it, but I never had one of those that lived, so I can not show you a picture. I have the Maid of Orleans now and that is like a weed.
I lost a big one this winter in the greenhouse because of the weather changes. I have the Star, which I am sure it is not, and the Maid has tiny flowers that turn white and they are small in comparison to the one you have.
This is the Maid, can you enlarge them and look at the flowers?
This is the Star or Royal (some growers call it Royal, others Star, it is basically the same plant) It is also called Confederate
I hope this helps. Wish I could come down and look at it. I could use some warmer weather.
