Bruce Willis' wife doesn't know if he is aware he has dementia.

The 'Die Hard' actor's loved ones revealed in February he had been diagnosed with degenerative condition Frontotemporal Dementia (FTD), a year after he stepped away from acting due to communication disorder aphasia, and Emma Heming Willis admitted she isn't sure how much the 68-year-old star understands.

Asked if he is aware of his condition on 'Today', Emma told co-host Hoda Kotb: "It's hard to know."

The 45-year-old model - who has daughters Mabel, 11, and eight-year-old Evelyn, with Bruce - admitted her husband's condition has been "hard" on everyone around him, including his three adult daughters with ex-wife Demi Moore.

She grew emotional as she said: "What I'm learning is dementia is hard.

"It’s hard on the person diagnosed, it’s also hard on the family. And that is no different for Bruce, or myself, or our girls.

"When they say this is a family disease, it really is."

Emma admitted coming to terms with Bruce's condition has been "the blessing and the curse" but she's thankful he was able to get a definitive diagnosis.

She said: "To finally understand what was happening so that I could be into the acceptance of what is — it doesn't make it any less painful, but ... just being in the know of what is happening to Bruce makes it a little easier."

The Make Time Wellness founder described her spouse as the "gift that keeps on giving" and him and his condition have taught their daughters a number of qualities such as "love, patience and resilience".

She said: "It's teaching them so much and how to care and love, and it’s really a beautiful thing amongst the sadness."

As well as looking after her husband, Emma is aware she needs to take care of herself too.

She said: "It’s important for care partners to look after themselves so that they can be the best care partner for the person they’re caring for."