Supermodel Tyra Banks and her husband, Norwegian photographer Erik Asla, have welcomed their "miracle baby boy" after years of struggling of being not able to have one due to infertility.

On her Instagram account, Banks posted that they now have a child, thanks to a gestational surrogate who carried their baby. Under this arrangement, the harvested eggs from a mother are fertilised with the father's sperm and the embryo is placed in the uterus of a gestational surrogate, who carries the baby until birth, according to WebMD.

"The best present we worked and prayed so hard for is finally here. He's got my fingers and big eyes and his daddy Erik's mouth and chin," wrote Banks, 41. "As we thank the angel of a woman that carried our miracle baby boy for us, we pray for everyone who struggles to reach this joyous milestone," she wrote. "York Banks Asla, welcome to the world."

Asla also posted "Witnessing the dawn of life is quite possibly life's greatest gift."

The host of "Tyra Presents FABLife" told People magazine last September of her desire to have children, according to Gospel Herald.

"Since I was 24, I used to say every year, 'I will have kids in three years.' I kept saying it over and over again. Because my business is very entrepreneurial. I'm not for hire, so I have to do everything. I kept trying to find that time for that to happen," she narrated.

She said undergoing in-vitro fertilisation was not easy.

"When you're like, 'OK, I'm just going to do it,' then it's not so easy as you get older," Banks said.

She added, "I've had some not happy moments with that, very traumatic moments. It's difficult as you get older. It's not something that can just happen."

Last September, she opened up with co-host Chrissy Teigen about the pain of infertility during a segment on "FABLife."