At least three billionaires, a smattering of celebrities — including a husband of “Real Housewives” fame — and an English lord.

Those of some of the bidders who were ready to compete Friday night in a once-in-a-lifetime auction of Al Capone’s personal effects — including his favorite pistol.

That’s according to Brian Witherell, head of the Sacramento-based auction house that’s been tasked by Capone’s three granddaughters with overseeing the sale of 174 lots.

Other items include gold-and-diamond-encrusted jewelry emblazoned with his initials, furniture, family photos and a letter Capone wrote from Alcatraz to his only son, Sonny.

The invite-only affair was set to kick off at 8 p.m. Central Time at a private club in Sacramento, but bids were also being accepted online and by phone from the 1,034 pre-registered bidders that Witherell vetted and approved.

Bidders hail from all 50 states and countries including France, England, Australia, Turkey, Hungary, Switzerland, Canada and Brazil.

“I’m slightly overwhelmed keeping track of all the bidders, but I can tell you Chicago is by far the most represented among the group, we have two people who flew out for the auction tonight,” he said, noting there were a total of about 50 bidders from Chicago.

About 150 bidders plan to attend the auction in person, he said. There will be no live video feed of well-heeled paddle raisers, but the public can track the real time progress of bids at liveauctioneers.com.

The starting bid is $50,000 for Capone’s .45-caliber Colt model 1911 semi-automatic pistol, his “favorite” weapon, according to the auction house.

Witherell said he’s already received multiple six-figure offers for the gun ahead of the official opening of the auction.

Witherell knew of only one potential bidder who was okay with being named — Craig Showalter, a physician from the Glenview area who specializes in addiction medicine. He planned to bid by phone.

“It’s hard to find anything relating to Capone that’s genuine,” said Showalter, a collector who previously paid $5,000 for an item with Capone’s signature.

“Every once in a while you see something that supposedly belonged to Al Capone come along with some letter from someone who was a friend of the Capone family claiming it was his, but you never really know,” he said. “But with this auction, it’s almost certainly genuine, and genuinely Capone’s.”