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Rachael Leigh Cook

Rachael Leigh Cook and her husband Daniel Gillies have separated after nearly 15 years of marriage.

The She's All That star, who shares two children with her spouse - five-year-old daughter Charlotte and four-year-old son Theodore - broke the news to fans in a heartfelt post on Instagram on Thursday, which she captioned with a heart emoji.

"With deep gratitude for every year we have spent together and the thousands of beautiful memories shared, we have mutually decided to separate as a couple," the 39-year-old wrote. "This decision isn't one we have come to easily or lightly.

"We love and respect each other as parents, people and artists and look forward to maintaining the best parts of our relationship for many years to come."

Concluding her post, Rachael added: "Your discretion in this matter is kindly requested for the sake of our children during this time of transition. Thank you to those of you who are already aware; for your tremendous compassion and understanding. Lots of love, Rachael and Daniel."

Daniel, 43, also uploaded a message to his Instagram page.

Previously, Rachael opened up about her marriage in 2013 after confirming her first pregnancy.

"We got married incredibly fast. We got engaged after dating for maybe five months and we got married a couple of months after that," she told People of waiting to start a family. "There was just so much more both of us wanted to do. We wanted to travel and accomplish a lot more in our professional lives."

The couple began dating in 2001 and married in August 2004.