Stephen Clements was 46.
The broadcaster had presented the 10.30 am to midday Stephen Clements Show on the station since September.
The married father of two began his radio presenting career on Citybeat, and then hosted Q Radio’s Breakfast Show for seven years.
Before working in radio Mr Clements, studied geography at university and lived in South Korea for a period teaching English.
BBC Northern Ireland controller Peter Johnston said: “We are sorry to bring you the sad news of the passing of our colleague Stephen Clements.
“Our thoughts are with Stephen’s family, friends and colleagues, at this difficult time.”
Stephen Clements began his full-time career as a radio presenter in his late thirties and quickly became highly popular.
The Q Radio breakfast show became one of the most-listened to radio programmes in Northern Ireland during his time there.
In June 2019, Mr Clements announced that he was leaving the station to join BBC Northern Ireland.
He subsequently co-presented the BBC NI TV series Open for Summer during the Open Golf Championship in Portrush in 2019.
He also co-hosted BBC Northern Ireland’s Children in Need programme in November 2019 with Holly Hamilton.
Mr Clements took over Radio Ulster’s mid-morning programme from veteran presenter Sean Coyle in September 2019, saying it had always been his “dream” to work for the BBC.
He is survived by his wife and two children.
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