He said: "We cycled through the South of France many years ago and fell in love with that style. It's all French Provencal - a beautiful French country house.
"We loved it. We built it. It was our dream home and we built it as a family home and we still love the place. We're really excited that they found a wonderful home in Montecito."
Terry designed every detail of the property - which boasts features including 16 bathrooms, a spa, library, arcade, cinema, gym, and games room - and even "scented" the wine cellar by tipping out cheap bottles of red onto the floor.
He told the Mail on Sunday newspaper: "I designed the wine cellar. It's a beautiful room. It's got gravel on the floor and I emptied a couple of cheap bottles of red on to the gravel so it smelled correctly. I thought that was kind of fun.
"My brother owns a plywood mill. Most houses don't have 11-ply wood and that's why the floors don't creak. I'm a bit of a fanatic about details like that."
The house has a state-of-the-art heating and ventilation system, which was built to sense fog coming in off the ocean.
Terry explained: "We used an algorithm to figure out when the heating system should shut down or spool up, based on the rate of change in the fog. We have sensors for sunlight on the south-facing wall to figure it out."
And the former owner thinks the privacy of the estate was likely a big draw for Harry and Meghan, who have 15-month-old son Archie together.
He explained: "The original 200-acre Riven Rock estate is off one of the main roads in Montecito and then you're off on another sub-road and you're in this private park-like setting, which is truly amazing. It's what hooked us on the property in the first place, the privacy of it.
"It was just calling out for a beautiful home to be built on it."
Terry thinks the royal couple got a "great deal" on the £11 million (NZ$22m) abode.
He said: "When we heard the news, we said, 'Boy, did they ever get a great deal', and secondly the quality is the finest. I'm pretty proud of it."
