A billionaire former bond trader once accused of putting dead fish in air vents to get back at his ex-wife is involved in a new stink — this time with his 31-year-old rocker son.

California financier Bill Gross is scrambling to thwart youngest child Nick’s auction of five 1918 “Inverted Jenny’’ postage stamps, which could fetch up to $3.4 million if they hit the block as scheduled Friday, sources told The Post.

Gross — also a world-renowned philatelist who even endowed a gallery at the Smithsonian Institution for stamp-collecting — claims that he gave each of his three kids some of his priceless “Jennys’’ about seven years ago, telling them that the stamps were to be kept as an inheritance for his grandchildren, a source close to the dad said.

The 24-cent postage stamps are some of the most coveted in the world thanks to a printing error that put the image of a “Jenny” biplane upside down.

Only one sheet of 100 was ever made before the error was discovered — and single “Jenny” stamps in good condition have fetched upward of $1.5 million at auction.

Nick Gross, a musician who has produced songs for Wiz Khalifa, is now planning to peddle a block of four “Jennys,’’ as well as a single of the stamp, through the auction house Spink.

He disputes that his dad ever put restrictions on selling them.

“There was never an agreement that the stamps would not be sold,” Nick told The Post in a statement.

“This is another example of my father’s bad and vindictive behavior, which is why I’ve had to distance myself from him. If he would like to have the stamps back, he is welcome to buy them at auction.”

The father and son have been estranged since Nick’s mother, Sue, filed for divorce from Bill in 2016, after more than three decades of marriage.

Sue claimed in court papers that her ex, who founded PIMCO — the Pacific Investment Management Co. — left their home in Irvine Cove, Calif., a smelly mess at the time, leaving empty bottles of “puke” and “fart” smells in the garbage and dead fish in the vents. Bill denied the accusation.

Bill, who has two other children from a previous marriage, was caught off guard last week when he learned through another collector that Nick was selling the “Jennys,” said the source close to his camp.

Nick has been the drummer for the rock band Open Air Stereo, which was featured on MTV’s Laguna Beach, and is currently playing with another group, Half the Animal.

His dad is now “exploring options’’ to keep the stamp sale from going through, the source said.

Bill first came to stamp collecting as a child, when his mother had given him a book of stamps that would help him pay for college — only to find out later that the stamps were worthless, he has said.

Since then, he’s become one of the most well-known stamp collectors in the world, having amassed a collection that included every stamp the United States produced from 1847 to 1869, and five of the six known four-stamp blocks of Jennys, plus singles of the valuable stamp.

Bill has been selling off parts of his stamp collection since about 2006 and donating the proceeds to his charity, which is named after himself and his two children from his first marriage, Jennifer and Jeffrey.

But Bill has had a sentimental attachment to the “Inverted Jenny” stamps.

“Never sell the ‘Inverted Jenny.’ Keep the ‘Inverted Jenny,’ ” he told Bloomberg TV in a 2016 interview.

Still, he has parted ways with a few. In 2005, he bought a block of the Jenny stamps for about $3 million — only to trade it for a single, rare “Z-Grill” stamp of Benjamin Franklin, only two of which are known to have been made.