It is understood that the original home at the rear of the property has sold and the other house, billed as having "vintage vibes" and marketed asking for inquiries from $1,750,000, is under offer.
Key snapped up the property, which sits in the Mt Albert Grammar zone, for $1.4m last June, which was 22 per cent about its council valuation at the time.
Azel Saralaeva from Ray White said that potential buyers had noted the high quality of the renovation and it attracted a lot of comments. "It wasn't a rush job. It was definitely one that was taken with a lot of skill and care."
Yesterday Key announced that he had sold a property in Glen Innes that he converted to three townhouses.
He was praised for the execution of the renovation by some online.
"Did a great job turning 1 ugly house into 3 beautiful homes for first-time buyer," one person wrote on Twitter.
"Could have built 3 x 3 storey monstrosities. Well done, they are cute!"
Another took a dig at the Labour Government's efforts in the housing market, writing: "That's how you do KiwiBuild".
These sales are unlikely to be the last for the son of former Prime Minister Sir John Key.
Max Key is listed as the director of multiple companies with an apparent interest in property development.
In his post to social media celebrating his Glen Innes sale, Key hinted at his future moves.
"But after hours of blood, sweat and anxiety-ridden tears, I can proudly say we've sold our first development and are progressing into bigger and better things," he wrote.
"On reflection, this project not only taught me about the intricacies of the industry but the qualities within myself. Thank you to all the contractors, family and friends who supported us throughout, I can't wait to see what the future brings for MTK Capital! Onwards and upwards!"
Champagne lifestyle
Video posted online showing one of the homes on the Glen Innes section gives a glimpse of the sort of property being developed by the young mogul.
It shows a well-appointed home with restrained styling - and a touch of luxury.
As the camera sweeps through the small property we glimpse a bottle of Taittinger champagne on the table before we glimpse, through leaded windows, an outdoor setting complete with imported sparkling water.
There was criticism from some that Key was only able to make his property moves due to his privileged position, but others disagreed.
"He has actually done a nice job," said another support on Twitter. "There is no need to rag on him because he has a rich family."