There was never any doubt.

But it has to be said: Bill O’Reilly has done it again.

In writing his 18th New York Times bestseller, he has landed his 11 for 11 No. 1 debuts in his “Killing” series of historical thrillers on Friday.

“Never thought I'd have a single No. 1 bestseller, much less 18,” O’Reilly told Secrets.

“Only in America, land of opportunity if you're willing to work for it. We are,” he said of himself and co-author Martin Dugard.

Their latest is Killing the Killers, a book about the global manhunt for the 9/11 killers and mastermind Osama bin Laden.

The book, published by St. Martin’s Press, was released 10 days ago and features information about the attack from intelligence sources and others that put a fresh spin on one of the worst days in U.S. history.

Having their 11th No. 1 hit on a book tied to 9/11 made writing it up a bit of a literary tongue-twister for the St. Martin’s team. Here’s how they presented it to us:

A perfect 11 for 11. KILLING THE KILLERS, the 11th book in the series, is now the 11th #1 New York Times bestseller. Sales in this series are roughly 19 million copies worldwide, and have spent close to 340 weeks on the New York Times bestseller list.

The "Killing" series has focused on the biggest historical events, including the deaths of Abraham Lincoln, John F. Kennedy, and Jesus.

O’Reilly also scored several other No. 1s with books, including one on former President Donald Trump.