Hadid, 52, opened up about the unexpected breakup during an appearance on Tuesday's Watch What Happens Live.
When host Andy Cohen asked at which point during shooting Hadid knew the marriage was over, the Dutch model–turned–reality star revealed she "didn't know until it was ended – until Nov. 15."
"We had already wrapped shooting, and the show was done," she continued. "I know exactly the day: Nov. 15." (Extra footage for the finale was filmed later and featured a heartbroken Hadid admitting "divorce is like death" on Tuesday's episode.)
As for where the relationship stands and how much the two exes communicate, Hadid said, "We are in touch a little bit, here and there."
After nine years together, the couple announced their divorce exclusively to PEOPLE on Dec. 1, the same day of The Real Housewives of Beverly Hills' season 6 premiere and to the shock of many of Hadid's costars.
On Tuesday's WWHL, Cohen also aired a preview of the upcoming RHOBH reunion, in which he questions Hadid over whether her battle with Lyme disease played a factor in ending their marriage.
"You can't underestimate how much it takes for a man to take care of somebody that's sick all of the time," Hadid said. "David didn't change – I'm the one that changed. And, you know, I guess this is the outcome of that."
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What about the criticism Foster received "for not wanting to be with you while you were sick," Cohen asked.
"I don't think anybody should criticize that," she said.
That being said, she admitted she felt "blindsided."
"I didn't think that was the end of the road," she added. "I would have hoped to wait until I got 100 percent well."
Part one of The Real Housewives of Beverly Hills reunion airs Tuesday at 9 p.m. ET on Bravo.