According to papers obtained by celebrity website TMZ, Nicollette, 52, is ending her marriage to Aaron, and the documents state that the couple went their separate ways a month ago.
The news has come to a shock as many fans, as although rumours of a proposal were rife, neither Nicolette or Aaron had announced that they were married.
The actress, who is best known for her role as Edie Britt in Desperate Housewives, has been married once before, and had two additional previous engagements.
She wed actor Harry Hamlin on September 7th 1991, but the marriage sadly ended less than a year later in August 1992, when he filed for divorce.
Nicollette later began dating Swedish personal trainer Nicklas Söderblom in 2004 and got engaged to him on New Years' Eve of the same year, but the pair called off the engagement in October 2005.
Nicolette in her role as Edie in 2004
She also became engaged to Michael Bolton, whom she first dated in the 1990s, in March 2006, but the engagement ended in August 2008.
Aaron and Nicollette were first spotted out and about together in December 2014, and although they kept their private life mostly under wraps, their relationship has been public knowledge ever since.
Earlier this year, a source told gossip site Humbesh that the couple may soon marry, saying, 'Nicollette and Aaron are very much in love and they might get married anytime this year.'
'She has fallen in love several times. But she thinks her love for Aaron is something different from anything she has felt before. She believes her love to be true and she considers her boyfriend quite special.'
'This is the reason why the actress does not want to wait too long to get hitched.'