Bruce Willis' wife has shared an emotional update on his dementia diagnosis.

Earlier this year, it was revealed that the Die Hard star had been diagnosed with the devastating disease, and was retiring from acting.

Since then, his family have shared several updates, posting videos and photos of Willis with his children and celebrating his birthday.

And now, the 68-year-old's wife, Emma Heming Willis, has posted a video about their daughter, Evelyn, and how she is dealing with her dad's illness.

Starting the video, Emma said: "So I have to tell you this story, and I’m going to try and do it without crying.

"Because when Evelyn told me this story, I was an absolute puddle.

Instagram/@emmahemingwillis

"Okay, here we go. So Evelyn says to me the other day, did you know that people with dementia can become severely dehydrated?

"And I said, 'Oh', I said, 'I didn't know that'. I said, 'But how do you know that?' And she says, 'Well, I was at school the other day, and I had some free time, and I was looking at fun facts about dementia'.

"Now, that's not funny, but it's kind of funny. And she really is her father's child because these two love some just random facts.

"So I said to her, I said, 'OK, Evelyn, we will always make sure that daddy has a bottle of water in hand. Thank you for letting me know'.

"And I said, 'But you know, that is the most loving and compassionate thing that you can do is to be curious and educate yourself on your dad's disease.'"

She added: "It really is one of the most loving and compassionate things that we can do as caregivers as friends, family, is to educate ourselves about our loved one's disease so we can best show up for them and support them in the best way possible."

Instagram/Rumer Willis

Since posting the video, it's been viewed countless times, with many praising Emma for being so open about their journey.

One user said: "Truly is a FAMILY disease.. Bless you all!!"

Another commented: "Dehydration is so prevalent in dementia. Do what you can to keep your loved one hydrated (water, juice, etc) throughout the day.

"It is amazing to see the difference it makes in their cognitive ability (even when that ability is decreasing)."

"It is a very difficult thing to go through," put a third. "My mother passed with dementia!

"Your daughter is correct she died from a clot to her lungs from dehydration and inactivity."

While another added: "An extremely smart young lady, it makes my heart full she is educating herself."