Yolanda Foster Opens Up About What Led to Split From David Foster

— -- Yolanda Foster admits that her chronic Lyme disease played a role in the breakup of her marriage from David Foster.

The "Real Housewives of Beverly Hills" star shocked fans a little over a week ago when she announced the split from her songwriter-record producer husband of four years. She opened up Tuesday to Andy Cohen on "Watch What Happens Live" about why they decided to divorce.

"You know we had a beautiful love story that I will treasure forever," she told Cohen by phone. "Unfortunately, it was not strong enough to withstand the circumstances that came our way."

When Cohen asked whether her Lyme disease played a role, Foster admitted that it made things more difficult for the pair.

"Well, chronic long-term illness is extremely challenging," Foster said. "Not only for the person sick but also for the caregiver. It for sure changed the dynamic of the relationship."

Foster did not linger on the problems of the marriage, however. Instead, she praised their time together.

"The truth is that we both worked through the difficult time through the best of our ability, so rather than judging what went wrong, I pick to honor the great times that we shared the last nine years. There were a wealth of good times," she said.

The former supermodel, 51, has suffered from chronic Lyme disease since 2012. She told Cohen that she is doing better since the last time she saw him.

"I have about 60 percent better brain function than I did in the last year," she said. "I can still only live and plan one day at a time. The exciting thing is watching the episodes and inspiring me, and I could see the progress that I have made. I am excited and grateful for that. I will continue to fight for a full recovery."

The couple announced they were ending their marriage Dec. 1.

"Sadly, we have decided to go our separate ways," they told People magazine. "We've shared nine beautiful and joyous years together. During that time we experienced love, friendship and the inevitable challenges that come with managing a marriage, careers, blended families and health issues."

This was the second marriage for the reality-TV star, who was married to Mohamed Hadid for eight years until their split in 2003. They have three children: Gigi, 20, Bella, 19 and Anwar, 16.

It was the fourth marriage for the record producer, 66. He has five daughters.