James Van Der Beek Won't Be at 'Dawson's Creek' Reunion

James Van Der Beek is canceling a highly anticipated appearance at a "Dawson's Creek" reunion event amid his cancer battle.

Van Der Beek, 48, shared on Instagram that he won't be at Monday's event, a reunion featuring Katie Holmes, Joshua Jackson, and Michelle Williams staged to raise cash for F Cancer in light of Van Der Beek's stage 3 colorectal cancer diagnosis.

"This is the evening I’d been looking forward to MOST since my angel Michelle Williams said she was putting it together, way back in January," he began his post. "So you can imagine how gutted I was when two stomach viruses conspired to knock me out of commission and keep me grounded at the worst possible moment."

"Despite every effort… I won’t get to be there. I won’t get to stand on that stage and thank every soul in the theater for showing up for me, and against cancer, when I needed it most."

The news was not all bad: "But I DO have an understudy. A ridiculously overqualified replacement who would have been #1 on my wishlist (had I ever dreamed he’d be available). Someone my kids would definitely consider an upgrade over me… Plus, he already knows how to get to the theater. So that’s convenient. The role of 'Dawson', usually played by James Van Der Beek…Will be played by Lin-Manuel Miranda. Can’t believe I just got to type that."

Ending his post on an upbeat note, Van Der Beek wrote, "Everyone please enjoy all the love in that room. Shine some on my family. I will be beaming and receiving from afar in a bed in Austin. And thank you @lin_manuel . You were a hero to my kids before… now you’re a demigod 😇."

The event will go on as planned at NYC's Richard Rodgers Theatre, and will also feature "Dawson's Creek" creator Kevin Williamson and actors Mary Beth Peil, John Wesley Shipp, Busy Philipps, Nina Repeta, Mary-Margaret Humes, Kerr Smith and Meredith Monroe.