The Hollywood actor released a statement on Tuesday afternoon (29 September) confirming the death of Cathriona, a make-up artist who was born in Ireland but lived in Los Angeles.
"I am shocked and deeply saddened by the passing of my sweet Cathriona," he said.
"She was a truly kind and delicate Irish flower, too sensitive for this soil, to whom loving and being loved was all that sparkled. My heart goes out to her family and friends and to everyone who loved and cared about her. We have all been hit with a lightning bolt."
According to reports from the US, the make-up artist was discovered dead at her home in LA yesterday after friends called around to check up on her.
The Los Angeles Police Department have not provided any further information at this time, but multiple outlets are alleging that Cathriona took her own life. Coroner Ed Winter told The Telegraph that a drug overdose is suspected at this stage but a conclusion of suicide cannot be confirmed just yet.
A statement from the coroner's office read: "She was found by a couple of friends who were concerned for her. They discovered her at her residence some time after 8pm last night. They called 911. It was reported as a suicide. Evidently there was a note which either referenced Mr Carrey or was addressed to him."
Multiple outlets are reporting that Cathriona's final tweet was posted on 25 September and read: "Signing off Twitter, I hope I have been a light to my nearest and dearest. [Love] to you all."
It's believed that Jim, 58, met Cathriona on a movie set in 2012 and they dated throughout 2013 before splitting. They had been pictured together earlier this year, however, fuelling rumours they had rekindled their romance.
Jim's most recent tweet, posted 17 September, featured a photo credited to Cathriona.
Grand Central, NYC. ;^}— Jim Carrey (@JimCarrey) September 16, 2015
(photo by Cathriona White) pic.twitter.com/N8QbQQDFLu