A man trying for a baby with his partner was also having sex with a 14-year-old girl _ and got her pregnant instead.
When the child was born the man denied being the father until DNA testing proved he was the biological parent.
Caleb Knauf, 22, appeared in the Masterton District Court on Monday before Judge Ian Mill and pleaded guilty to unlawful sexual connection with a young person.
After giving birth both the girl and Knauf denied it was his, but a police-enforced DNA test proved otherwise.
Crown prosecutor Geraldine Kelly said Knauf became a trusted family friend of the girl's family in 2011.
At the time the girl was only 13 and they soon formed a relationship, socialising together, Ms Kelly told the court.
The girl's mother confronted them about the relationship.
"He'd seek out opportunities to be alone with the young girl ... they were caught in bed together but he denied any wrongdoing.''
In 2012, Knauf formed a relationship with an older woman who was known to the girl and they were trying to have a baby together.
But in July last year, the victim, then 14, gave birth to a son and Child, Youth and Family became involved with the family, Ms Kelly said.
Police successfully applied for a compulsory DNA order which identified him as the father, she said.
"Both the girl and he denied he was the father ... he then admitted they had fallen in love ... the baby was to be a surrogate for [his partner].''
Convicting Knauf of the charge, Judge Mill served him with a first strike warning about the consequences of future sexual or violent offending.
If he is convicted of a second sexual or violent offence he will be jailed without parole. If he commits another of the 40 crimes listed against the three strikes warnings he will be jailed for the maximum term for that crime and serve it without parole.
Knauf was remanded on bail for a pre-sentence report and is due to be sentenced in Hutt Valley District Court on June 18.
- By Cherie Taylor of the Wairarapa Times-Age
