First son Max Key has celebrated his landmark birthday with a superheros and villains-themed party at the Prime Minister's Parnell mansion last night.

A relaxed-looking Key, dressed at Batman, posed for photos with fellow good guy Superman and villains such as The Joker in photos of his 21st birthday bash posted on Instagram.

Among the A-lister young set in attendance was Bachelorette Erin Higgins.

Even Max's dad, Prime Minister John Key, joined the fun, albeit in a dress shirt rather than superhero or villain costume. The PM was also photographed posing with two female guests in Batgirl costumes.


Earlier this week, Max Key thanked birthday wellwishers and promised his many social media followers something big was on the radar.

The university student and aspiring DJ turned 21 on Wednesday and posted a thank you message alongside a photo of himself posing next to a black Ferrari.

"This year has been the busiest of my life and also the most challenging. In saying that, I can't wait for what's to come, and in particular the next few weeks. There's something on its way," he wrote, likely referring to the racy video he's filming for his second single.

Key's first single as a professional DJ - Forget You - reached the New Zealand Viral 50 number-one slot on Spotify a week after its February release.

The PM's younger child has also been busy posing for a series of shirtless photos for Remix magazine's Winter issue, out next month.