Remind me who that is (or where she's referenced in SKT), doesn't ring a bell at all.
Sirac is one of the playable NPCs in Bryn Shander. He's the one pinging on the frost giants'
blod stone radar. SKT says he's the son of Artus Cimber, and that his parents (plural) essentially abandoned him when he was little, so he grew up on the streets of Suzail in Cormyr before heading up to Icewind Dale, where he found religion.
However, back in the 2e days, Artus Cimber fell in love with
Alisanda Rayburton, the daughter of the Cormyrean adventurer who had the
Ring of Winter before Artus, and married her. Alisanda is actually a lot older than Artus, as she and her father became immortal barae (protectors) of Mezro in Chult several hundred years before Artus was even born.
Anyway, Alisanda was still in Mezro when it was supposedly destroyed during the Spellplague, although we now know, thanks to ToA, that it was just whisked away to some other dimension. Alisanda has been trapped there ever since, and after waiting around for a century, Artus is now trying to find a way to bring her back.
Alisanda can't be Sirac's mother unless he is also more than one hundred years old, but SKT seems to suggest that that isn't the case. Therefore, despite the fact that Artus clearly loves Alisanda enough that he is seeking to reunite with her, it would appear that he was unfaithful to her at least once, resulting in a love child that neither he nor the other woman wanted to raise themselves.
With all that in mind, I think it makes more sense for Sirac to merely be a (distant) blood relative of Artus, rather than his son. Sirac just happens to be the closest member of the Cimber family to the frost giants'
blod stone. If the giants were to visit Cormyr, they'd probably find more of them.
EDIT: Some relevant quotes:
SKT, p 39:
"Sirac knows that he's a son of the immortal Artus Cimber and thus carries the Cimber bloodline, not that it has ever benefited him. Artus's immortality, it is said, comes from a magic ring--a ring that Sirac has never seen. Sirac's parents gave him up as a baby ..."
ToA, p 212:
"A former member of the Harpers, Artus Cimber is the keeper of the Ring of Winter
. He found the ring in the jungles of Chult, where he also met his wife, Alisanda ... Artus has spent most of his life trying to keep the Ring of Winter
out of evil hands, but his return to Chult is focused on reuniting with his beloved Alisanda, who disappeared along with the city of Mezro during the Spellplague. No longer content to wait for Alisanda and Mezro to return on their own, Artus has been seeking the means to bring them back."
