U.S. broadcasting channel Freeform announced that the show will be ending after its third season.
The show, which airs weekly on Netflix in Australia, will have two-hour series finale in 2019 to say goodbye once and for all.
Katherine penned a lengthy letter to her fans, writing in the caption, "Hail and farewell, Angels..."
"We just found out too - and believe me we are as shocked as you," she began. "I fell in love with this story and it's mythology instantly. Playing Clary has been an honour and a joy," she continued.
"I promise you this," she finished. "By the angel, will make you the most rock solid, bad ass, magical finale you could imagine." CRYING!
Dominic shared similar sentiments.
"All good things come to an end. It has been my privilege to be a part of this world. @ShadowhuntersTV team have been so close to my heart for 3 years. You. The fans. Make us happy and strong and proud. Thank you. For everything. We say goodbye with a heavy heart but our heads...
"...held high. We love you. Forever and always. Xx"
Matthew Daddario called it "a sad day."
"This is a sad day but I am cracking up at your love for birds of paradise... and chickens. Never change guys. See you out there!"