The FTD Brothers, Jordan and Cian Adams, on day 12 of running a marathon a day, in County Leitrim.FTD Brothers / Instagram
The two brothers have raised over €1.3million for their cause after being diagnosed with "early-onset" FTD.
Both men carry a gene that was passed down by their mother, Geraldine, who passed away in 2016.
This means that Jordan and Cian, who are from Redditch in England, are 99% likely to contract the condition and develop symptoms in their 40s.
Last month, Jordan ran the London Marathon with a 25kg fridge on his back, before flying over to Ireland for a new challenge.
The 30-year-old is running 32 marathons in 32 days to raise funds and awareness of dementia, with support from his physio brother.
The Prince of Wales has since sent a message of support to the pair, which was read by their father, Glenn, on Sunday morning.
The Prince of Wales, William.
William wrote: "Taking on such a demanding challenge, to honor your mother’s memory and raise awareness of frontotemporal dementia, speaks to your remarkable strength.
"You are inspiring people far beyond those who stood along the marathon route here in London, and those who will no doubt be cheering you on along the roads of Ireland.
"It takes great courage and generosity to turn such personal adversity into hope for others.
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"By sharing your story so openly, you are helping to change understanding of dementia and giving countless families strength, comfort, and a sense that they are not alone.
"I hope you are both proud of all you have accomplished so far and wish you both every success for the road ahead."
The message arrived on the 14th day of the journey as the brothers reached Leitrim, the county that was home to many of the 12 Irish relatives they lost to FTD.
The challenge is set to conclude in Dublin on May 28.
* This article was originally published on Extra.ie.