An Auckland man felt "betrayed" after his partner of almost 30 years died and left him only her ashes, sparking a legal battle over the meaning of a de facto relationship.

A decision from Justice Grant Powell in the Auckland High Court, released on Wednesday, ordered that Steven Moon be paid $NZ300,000 ($276,000) out of the estate of Mary Doyle.

Their relationship had lasted for 27 years and ended with Doyle's death after a long battle with cancer early last year, the decision said.

Steven Moon laid claim to the whole of Mary Doyle's estate, which was opposed by her older brother. Credit:Alamy

Moon told the court that after Doyle died and he read her will, he was "very upset and felt used" when he found she'd bequeathed him only her ashes.