The actor took to Instagram to share a lengthy post Sunday about his diagnosis ... morning when I was informed that a tabloid was going to run with the news,” Van Der Beek wrote. “I’ve been dealing with this privately until now, getting treatment ...

I’ve been privately dealing with this diagnosis and have been taking steps to resolve it, with the support of my incredible family,” the ‘Dawson’s Creek’ star told ‘People.’

Kimberly Van Der Beek is there for husband James Van Der Beek following his cancer diagnosis. "I love you baby ," Kimberly, 42, wrote in the comments section of the actor's lengthy Instagram message regarding his health,