This Is Us left fans in tears with the final episode of 2019.
On This Is Us Season 4 Episode 9, fans were taken to the future thanks to a nine-month flash-forward that gave insight into Rebecca's battle with dementia.
Co-showrunner Isaac Aptaker has now revealed in an interview with TV Line that Rebecca actress Mandy Moore made sure they showed the condition in the most "authentic" way possible.
"For this one, I think it’s such a testament to Mandy and the work that she’s doing," he told the outlet.
"Remember, this is a woman in her 30s, who hasn't even had a family yet, who's now playing a grandmother dealing with dementia and this onset of stuff that doesn’t happen until much later in life.
"It's so far beyond Mandy’s own personal experience, so she's doing so much work as an actor."
Aptaker said that Moore made the effort to chat with experts on dementia, as well as "people who've been personally touched by this" ahead of the storyline being filmed.
"All those little details that she's bringing to the performance are the result of that research and the work that she is doing to accurately portray this," Isaac continued.
"It's really blowing us away."
The outlet subsequently asked about how Rebecca's illness could affect the rest of the family, but Aptaker wanted to stay quiet for the most part, saying that he doesn't "want to get ahead of our storytelling."
As for when the series will catch up to that flash-forward, Aptaker says that fans will be up to speed by the beginning of This Is Us Season 5.
"Everyone's questions about Rebecca and her status and how things have progressed will be answered."
With a show like This Is Us, the action generally takes place over different decades, but it's nice to know when we will have some solid answers.
What did you think of the emotional midseason finale?
Hit the comments below.
Remember, you can watch This Is Us online right here via TV Fanatic.
The series continues Tuesday, January 14 2020.
Paul Dailly is the Associate Editor for TV Fanatic. Follow him on Twitter.