Former Alliance party deputy leader Seamus Close has died after a short illness.
According to reports, it is understood Mr Close had suffered from liver cancer.
Mr Close, 71, served as a Lagan Valley MLA from 1998 until 2007.
Party leader Naomi Long said politics had lost an "advocate for ordinary people".
She said it was a "very, very difficult time" for his family.
"It was very sudden. He had been losing weight and felt particularly tired. It seems it was quite advanced and very little could be done," she told the BBC's Stephen Nolan programme.
"When he was in a room there was such an energy around him. He's such a big loss."
In 2006, Mr Close announced his retirement from politics, after 33 years and 20 elections.