I've got a question about the Holbein portrait called "Unknown Woman, formerly known as Catherine Howard" (NPG 1119) that is now at Montacute House. This is the portrait where the sitter is wearing a simple black or very dark green gown with gold trim and a high collar. It has a Latin caption in the background giving her age as 21. I've read that this sitter might be Jane Seymour's sister but never how this theory was reached. How was it determined that it wasn't Catherine and who proposed it?
[ed note - this is the portrait in question]