The sister of conservative Australian Prime Minister Tony Abbott has posed nude with her fiancé in a portrait to raise awareness of gay-marriage.

Christine Forster is pictured hugging her partner of six years, Virginia Edwards, in a painting created by Sydney artist Robyn Ross, for this year’s Archibald Prize, according to reports in MailOnline.

The couple, who have been engaged for nine months, were approached by Ms Ross with the portrait idea last year.

Ms Forster and Ms Edward collaborated with the artist and approved of the naked embrace depiction to highlight the marriage equality debate.

“We don’t have any problems with it being portrayed in that open and honest way – that’s what our relationship is about,” Ms Forster told the MailOnline.

“It’s very confronting to see paintings like that of yourself. You’re looking at something that is captured from someone else’s eyes.

“(It) blew us away and that’s pretty amazing.”

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Ms Forster, a liberal City of Sydney councillor, said she could imagine the Prime Minister reacting in the same way.

“I think he will think it’s a great artwork. Tony and I and Virginia and Margie (Mr Abbot’s wife) are close. We’re a family. We love each other,” she said.

“He will probably have the same response I had and that’s “what an incredible piece”.”

Ms Ross said the couple did not pose nude in front of her, instead they wore sarongs as she sketched and photographed them in her studio.

“The whole idea was to have no jewellery or clothing, just them. But it’s not a focus on them being naked – it shows two people in love in a pure and honest way,” Ms Ross said.

“It’s an intimate insight into two people in love. It doesn’t matter if they’re the same sex. They should be given the same right to get married.”

The Archibald entry, titled Ladies In Waiting, took Ms Ross about 75 hours to paint and stands at 1.5 square metres.

“I sketched them, took photos and discussed with them how to put it together,” Ms Ross said.

“We all decided on the concept that was going to send a strong message.”

This is not the first time the couple has posed for a portrait. Sydney artist, Perry Westwood, painted their first portrait when Ms Forster and Ms Edwards came out publicly with their relationship.

“I really think that two artists approaching us to paint us is a really strong indication of just how much marriage equality as an issue has been accepted by ordinary Australians,” Ms Forster said.

“It just reflects how much marriage equality and gay and lesbian issues are just part of the mainstream. It’s nothing unusual, it’s just a no brainer.”