Mr Mortimer's deep belief that his dad would love him unconditionally rang true on Saturday when he and his partner, Jason Palmatier, an emergency room doctor from America, sealed their recent marriage in Chicago by reciting their vows in the NSW central west township of Orange.

"Even though I didn't come out until I was 22 or 23, I knew deep down I'd never have a problem with dad because all he's ever wanted is for his children to be good people," Mr Mortimer said. 

The pair met not long after Mr Mortimer moved to Chicago in 2013 to work for the international advertising company Leo Burnett and they "hit it off immediately". 

"We just clicked and the family joke is I went over to the States and bagged an American doctor," Mr Mortimer said.

In a further display of unconditional love, Mr Mortimer's three uncles Peter, Chris and Glenn - who were rugby league heroes in the 1970s and '80s, a time when some say homophobia was entrenched in league's culture - also stood among the families and friends of both men as they professed their love for one another.

With his brother Peter's picturesque vineyard and the Australian bush as a stunning backdrop for the ceremony, Steve Mortimer said he and his wife, Karen, were ecstatic for their son.

"Matthew is creative, he has great principles and he works hard," said Mortimer, remembered as a passionate footballer who led Canterbury Bankstown and the NSW State of Origin team to numerous glories.

"His mother and I love him as we love his brother Andrew and sister Erin. When I look at him and Jason I'm happy to think he's met an incredibly decent person ... a great person ... who loves him."

Mortimer's advice to fathers who are struggling to accept their son's sexuality is simply to be there for them. 

"For anyone wanting to know what it is like to have been a supposedly tough footballer who has a gay son, my answer is simple: I love him," he said. 

"I hope any father who is having trouble accepting their son is gay will read about our relationship and realise you need to allow for your child to be who they really are, and just as importantly to respect them for who they are."

Dr Palmatier joked about how Matt offered an important tip that ensured his future father-in-law welcomed him into one of rugby league's most famous families.

"On one of my first trips to Australia I saw a football jersey I thought was pretty cool and when I told Matt I might buy it he warned I wouldn't be allowed into the family house because it was AFL -  it wouldn't be accepted," he said, laughing. "I didn't realise there was such an intense rivalry between the football codes."

Steve Mortimer said it was through his wife, who is one of Australia's most respected theatre directors, that he realised during his playing days that any prejudice against homosexuals was a result of ignorance.

"Having Karen work in theatre meant I met a lot of nice people who were friends of my wife and they happened to be gay," he said. "Getting to know them made me a better person."

Nevertheless, Peter Mortimer, whose son Daniel plays first grade for the NRL's Gold Coast Titans, said he's "in awe" of the way his eldest brother embraced Matt and Jason.

"Steve is from a very macho family but he's done everything possible to encourage Matthew to live his life and to also welcome Jason into our family in exactly the same spirit as we have other people over the years," he said. "I'm in awe of him. It says a lot about Steve as a person and a father."

The Mortimers steered clear of the gay marriage debate that is dividing Australia, preferring instead to note that Matt and Jason's union brought many people together, including 25 who made the trip from the US, proving love is strength, love is unconditional and love is born from love. 

"That is the message we want to share," Steve Mortimer said.