Alliance MLA Sorcha Eastwood has said her husband is being treated for an acute form of leukaemia.
She said Dale Shirlow will spend at least six months at a cancer centre, describing her partner as "fighting for his life".
The Lagan Valley MLA said the couple are "being strong even though my heart is breaking".
Read more: Alliance MLA Sorcha Eastwood steps back from election canvassing after husband's 'bad health news'
Ms Eastwood last month said her husband had received "bad health news" which led to her stepping back from canvassing for May's council election.
The couple married on the day of the June 2017 Westminster election, with Ms Eastwood voting at a polling station in her wedding dress.
Ms Eastwood on Thursday posted online an update on his condition.
She said: "Just an update on Dale for all of you who have been asking.
"We were called in today after the tissue biopsy had initially been inconclusive. But we were working towards a common lymphoma.
"Unfortunately we didn't get the news we were hoping for today.
"There has been something come up in the tissue sample that they didn't expect and Dale is now being treated for Acute Lymphoblastic Leukaemia T-Cell.
"He is being taken into the Cancer Centre either this afternoon or tomorrow morning for at least six months if all goes well. He is now fighting for his life.
"Obviously we are shocked and devastated but he is powering through and we are being strong even though my heart is breaking. Just wanted to keep you all in the loop.
"We will beat this!!!
"As ever, my office continues to be open for you all."
In a social media post last month, Ms Eastwood said she would have to "take things at a different speed as I care for my husband and prioritise family".
She thanked the South Eastern Health and Social Care Trust and the wider health service for their help.
The MLA said that staff "couldn't have been quicker and more supportive as we start to move through this journey", adding: "They are incredible people who are worth their weight in gold."
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