David Foster Says Wife Yolanda 'Is Doing the Best She Can' Battling Lyme Disease

This video is unavailable because we were unable to load a message from our sponsors.

If you are using ad-blocking software, please disable it and reload the page.

Music producer David Foster spoke to ET about his wife Yolanda Foster's battle with Lyme disease on the Emmys red carpet on Sunday.

"Yolanda is doing the best she can," David, 65, told ET's Nancy O'Dell. "She's on a mission and she's just going to keep trying until she finds a way to get better. It's been three and a half years and she just keeps trying."

WATCH: Yolanda Foster Says Ongoing Battle with Lyme Disease Is a 'Nightmare'

Yolanda, perhaps best known for starring in The Real Housewives of Beverly Hills, was diagnosed with the disease in 2012.

Last month, the 51-year-old reality star suggested that a rupture from a 20-year-old implant could be the cause of her chronic health issues.

"Turn a mess into a message ... We might have hit the jackpot by finding all this silicone from a 20 year old implant rupture through ultrasound mapping as shown in this selfie," she wrote in a message posted to Instagram. "Thank you Dr.Feng for holding my hand and leading the way #UncoveringTheMystery #ChronicLymeDisease #ExPlantSurgery @FengClinic #MyHealthJourney #DeterminedToFindACure."

In January, she revealed in a blog post for Bravotv.com that she had lost the ability to read, write or even watch TV.

WATCH: 'Real Housewife' Yolanda Foster Has Lost the Ability to Read or Write

Despite the toll that the disease has taken on her, Yolanda did seem to find some moments of fun and relaxation over the summer. In a photo posted to Instagram last month, she sat in a pool with her 18-year-old model daughter Bella Hadid.

"Mommy n meee day," Bella wrote as the caption for the pic showing mother and daughter in matching swimsuits. "Home is when I'm with you."