The couple announced the news 'with great sadness' in a statement on Twitter, revealing they are parting on good terms, with their 21-month-old son Ethan remaining their priority.
'It brings me great sadness to tell you that Kris and I have separated,' Dannii Minogue wrote.
'We still care for each other and ask for privacy at this difficult time, in particular for our son Ethan who remains our number one priority.'
After thanking fans for their messages of support, the singer said she needed to 'retreat for a while' to adjust to the news.
Meanwhile, Kris took to his own Twitter page, telling fans: 'Dannii and I have a deep mutual love and respect for each other and although things have not worked out we have a gorgeous son together that we both love and implore everyone to respect our privacy at this challenging time.'
Although the couple are yet to reveal the reason behind their split, everything from Dannii's ongoing work commitments to Kris's partying have been cited as the cause.
They were forced to deny reports of a split last year, after rumours about Smith's close friendship with model Lauren Phillips.
At the time, Dannii Minogue cryptically Tweeted: 'Never chase love. If it isn't given freely by another person, it's not worth having,' but Kris later countered talk, confirming: 'we are committed to our relationship and Ethan as always.'
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