Was given this as a small seedling 3 years ago and it was labelled Lady Isabel. Very strong plant with 4 flowers and 2 new growths but was just wanting views as to it's ID.
Especially if it is a more complex hybrid. We always tend to think of NOID hybrids from the perspective of a primary hybrid. I have a NFS seedling of Susan Booth x St Swithin. I would think a lot of seedlings from that cross would look like this, especially as this flower is darker than most St Swithin's I have seen. To be honest those petals look a lot like my Susan Booth, but it is not that cross. It could be more complex than a St Swithin.
I agree, a NOID is a NOID. I don't think you can be definitive with this.
Strongly St. Swithin, but as already pointed out a more complex cross cannot be excluded. Stunning bold dorsal markings and good colour, ... Looking good!