Blair, 50, recently opened up about how the former costars and close friends support one another after both were diagnosed with multiple sclerosis.
"She is an iconic California girl actress of my generation, and she is it," Blair continued. "There has not been one thing that she's done that I haven't been like, 'Nailed it,' and she's nailing just being who she is with this MS."
While the disease presents itself differently in those who are affected, some people go through life with only minor symptoms while others become seriously disabled.
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The National Multiple Sclerosis Society explains that the disease causes damage in the central nervous system that interferes with the transmission of nerve signals between the brain and other parts of the body. Because of the problems it causes with muscle control, symptoms can include numbness and lack of coordination.
Although Blair has been living with the invisible illness since October 2018, she told Entertainment Tonight that Applegate is her support system and "just a strong one."
"If you need something she's at your house. There have been things that I had been unglued, and she's like, 'I'm outside. Answer the door.' She's just amazing and strong and fun," she said.
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The recent Hollywood Walk of Fame honoree, in return, receives help from Blair with canes and things that help make living with the disease more manageable.
"She has a lot on her plate. It's a lot, but she's as brilliant and beautiful as ever," Blair added.