The 111-year-old tuatara, a resident of Southland Museum since 1970, lived a quiet life there until a high-profile sex romp with the much-younger Mildred in March.
His lover, aged 70 or 80, has since laid 12 eggs.
Museum staff said Henry had never shown an interest in mating but put his newfound desire down to a cancer growth being removed from his nether regions.
Museum tuatara curator Lindsay Hazley said Mildred laid 12 eggs on July 15 but one had since perished. The remaining 11 eggs were being kept in an incubator at between 18 and 21degC and were scheduled to hatch in about six months.
"The fact they have come this far is a good positive sign," he told the Southland Times.
"As each week goes by I get more confident the eggs will last."
He now expected Henry to breed every season.
The centenarian was currently enjoying the company of three females in his enclosure -- Mildred, Lucy and Juliet -- with the next breeding season in eight months.
"With these guys foreplay might take years. One has to be patient," Mr Hazley said.
The virile young Charles, aged 22, also fathered a clutch of 10 eggs about the same time as Henry.
In addition, another four or five tuatara were also expected to lay eggs this season, sparking a mini baby-boom at the museum.
