"Catherine's being quite open about it, because she was outed," said Douglas on Tuesday's The Oprah Winfrey Show, adding that Zeta-Jones had originally hoped to keep her health issue private.
And what else does the actor have to say about that? Plenty...
How did news that Zeta-Jones had checked into a Connecticut mental health facility for five days go public? The Wall Street star theorized that the invasion of privacy probably occurred when "some other patient probably said, 'Hey, you won't believe who's in here now.'
"So once that happens, I think she felt best to get out her story," he said.
Douglas admitted it's been a difficult year for the couple.
First, the actor was sued by his ex-wife, Diandra over royalties she claimed he owed her from Wall Street. Then his eldest son, Cameron, was sentenced to five years in prison on a drug conviction. And finally there was his own highly publicized battle with throat cancer, which resulted in five months of radiation and chemotherapy.
Douglas noted the hardest hit was his Zeta-Jones, who didn't have much of an emotional outlet during their "harrowing" ordeals, which worsened her depression.
"I think that part of Catherine's whole background. She's Welsh, and the Welsh it's all stiff upper lip, not let your feelings show," he said. "In my last year and a half my oldest son is in federal prison, my ex-wife is suing me and I got cancer. It's kind of hard for the wife to say, 'I'm depressed.'"
Hence, her decision to go for help, and later go public.
"If my revelation of having Bipolar II has encouraged one person to seek help, then it is worth it," she told People magazine.
"I think she's relieved because she has a much better understanding [of her diagnosis]," he added.
As for Michael's own health, the 66-year-old Hollywood legend choked up when the talk show queen asked if the cancer had changed him.
"Wow. . .I know that I'm much much closer to my friends and family, I have a much deeper appreciation of family and friends," he said. "I was truly overwhelmed by the support."
Douglas is next slated to reteam with his Traffic director Steven Soderbergh for the big screen biopic Liberace.