The owners of the 21st-floor super-unit at the Trump Parc at 106 Central Park South owe some serious cash to both the condo and the city.

The luxurious, 10-bedroom, seven-bath apartment atop the 37-story tower was purchased in 2013 for $14.25 million. It came with a separate apartment that is used as a private gym.

The prior owner was renting out the marble-filled spread for a mere $57,500 a month.

The new owners have increased the mortgage several times over the years, essentially using the grand pied-à-terre as a piggy bank.

In December 2016, they last refinanced with Citibank by adding an additional $4.56 million over its then-$13.65 million mortgage — to total $18.2 million.

Yet just one month later, in January 2017, records show two property tax checks to the city bounced.

As of Monday, the main residence owes the city $99,362 and the gym unit owes $6,387.

Although the city shows $12,874 in credits on one of the units going back to 2014, an application must be made to obtain these funds as the Finance Department doesn’t credit past-due bills or proactively send out a check.

New documents show the owners now owe the condo $34,034 for common charges and fees back to February.

According to sources and international records, the owners are a “nice couple” from Australia, so I’m hoping it isn’t a medical or financial kerfuffle and the bills were merely eaten by a neighborhood dingo.

Their lawyers did not return calls or emails for comment.

This appears to be the first time since 2013 that this board has had to file a lien — although a handful were previously filed in the Trump-developed tower.

The company declined comment.

Unfortunately, this building is not alone. A few high-priced apartments along Billionaires’ Row that were sold to foreign entities have since been foreclosed as their owners’ fortunes changed — or the individuals were sought for misdeeds in their homelands.

As once source advised, “This happens from time to time.”

Eventually the units are foreclosed and sold, the arrears paid, and the boards and other residents are made whole.