Singer and actress Candice Alley was warned not to sign a prenuptial agreement before she married former Olympic swimming champion Grant Hackett because it was "grossly unfavourable" to her, court documents reveal.

Barrister David Brown, QC, allegedly believed the agreement was one of the worst he had ever seen.

Grant Hackett and Candice Alley split in May 2012. Credit:Paul Rovere

In the original pre-nup, Alley – who recently joined Neighbours in a recurring guest role – was to get 15 per cent of Hackett's assets if their marriage broke down after less than 10 years and 25 per cent if they split after more than 10 years.

Hackett, 35, is suing Brisbane-based Mullins Lawyers and Melbourne-based Nevile & Co over the allegedly botched agreement, claiming their negligence caused him financial loss because it was found to be not binding.