The Last Hours (Theories)

Grace Blackthorn/Cartwright

What do we know so far about Grace (in chronological order) :

•Nothing But Shadows [12-year-old Grace]

"The only person who liked him (James) was a girl and nobody could know about Grace. Perhaps even Grace would not like him if she knew any other people"

"Not that James had any particular girl in mind. James told himself and crashed all thoughts of Grace; the secret girl. Grace, who needed to be rescued"

So Grace is a character based on Great Expectations' Estella. She was adopted by Tatiana Blackthorn and now it is confirmed that like Estella, she lived isolated in Tatiana's house in Idris. At this point I think she must have been adopted because in order to see her be so loyal to Tatiana (like we see her in the Midnight Heir) she must have spent her childhood with her and portrayed her as her mother.

"And if James was in Idris more often, he could perhaps see Grace more often too"

•The Midnight Heir [16-year-old Grace]

She appears in a long part of the story so I'll only use phrases or scenes that I want to focus on.

Grace also grew to have an unearthly beauty and is implied to possess siren-like abilities, both of which are exploited by her adoptive mother.
~Shadowhunters wiki

Magnus noticeably mentioned: unearthly gray eyes, she was made to attract attention but not express anything real, she was beautiful yes but also more than that, beauty unlike most humans, everything about her was perfectly structured to appeal

Also Tatiana says to Grace about Magnus: "And he is not mortal. He has lived for many years. One cannot expect him to have the normal reactions"

Will earlier on hearing that Magnus was called to enhance Grace's beauty he said that she doesn't look like a toad in a bonnet.

The events of TMH are set during TLH, so Grace enhanced her beauty for her mother's plan (probably). James Herondale was in love with her when little and because he doesn't visit Idris quite often it is a shock to him to see Grace to have grown and become so pretty.

We already know that she will break his heart and cause him severe heartbreak. I assume that ruining James' life is her mission, but Tatiana wasn't only vengeful over Will Herondale. She thought that her brothers betrayed her and killed their dad. So here is another theory of mine (yet I really don't want this to happen).

Grace marries Christopher Lightwood, Gabriel Lightwood's son (brother of Tatiana), as portrayed a Lightwood family tree and they had a son named Isidore. Maybe this is Tatiana's great revenge plan. Yet I Chris and Grace look like a couple with great potential.

Lastly, Cassandra Clare said that The Last Hours and The Dark Artifices will be connected (the same way like TID and TMI were). I have some thoughts on Grace's gray eyes, that I suspect are not natural. We also know that Tiberius Blackthorn from The Dark Artifices is the only one in the family to have gray eyes and they don't know from who he inherited the eyes from. Have also in mind that he has a twin who looks like the other Blackthorns (brown wavy hair, blue-green eyes) unlike him (black hair, gray eyes). Maybe it is a magical thing that they both share? It could be genealogical, it's not a theory based on clues, I just noticed the similarity between the two.