Talk about curveballs. Leave it to Danny McBride to let fly a doozy.

That was indeed multi-Oscar-nominee Bradley Cooper as a Civil War-era robber turned preacher in “The Righteous Gemstones,” whose fourth and final season kicked off Sunday (nine episodes airing weekly 10 p.m. EDT/PDT on HBO).

This flashback kickoff, which looks to tell the devious origin story of the megachurch-leading Gemstone clan, went from long shot to lock quickly.

“Bradley said OK, but he had never seen ‘Gemstones,’ and he didn’t want to, so as not to be influenced by it,” says McBride, who wraps a trilogy of pompous-protagonist series that include insufferable pitcher Kenny Powers in “Eastbound & Down” and his “Vice Principals” co-lead-buffoon (opposite Walton Goggins), Neal Gamby.

“What was amazing to me watching it after was just how much Bradley’s character seems like a Gemstone,” he says, adding a laugh. “He’s in line with how our Gemstone brethren act.”

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McBride says he loved being only a director on Episode 1, perhaps a hint of things to come. Despite the power of that gory kickoff – Goggins, who in “Gemstones” plays preacher Baby Billy Freeman, said “the script alone blew me away, it could be published as prose” – there is no return to the 1800s in the remaining eight episodes.

Instead, the manic thrust of this wrap-up season is getting the progeny of widowed patriarch Eli Gemstone (John Goodman) – Jesse (McBride), Judy (Edi Patterson) and Kelvin (Adam Devine) – to finally accept the death of their mother, Aimee-Leigh (Jennifer Nettles), and move on with their respective lives.

Kelvin and Amber Gemstone are among the ‘Righteous Gemstones’ who blossom in Season 4

Among those characters who come into their own finally are Kelvin, who has embraced his homosexuality and runs a gay ministry called Prism. “I was so happy Danny and the team took things in this direction, because we see my Gemstone siblings supporting me, while its other churches who are trying to take me down,” he says.

Also flowering this season is Jesse’s wife, Amber (Cassidy Freeman), who has mostly been dismissed by family members. “I love that she finally gets to be the mom she wants to be, connecting people, building bridges and reminding everyone that at the end of the day, family is all we have,” Freeman says.

If that sounds like serious fare, worry not. The episodes are packed with so much McBride-inspired lunacy that it’s hard to know where to begin.

There are the Prayer Pods, a Jesse brainchild that are promptly abused by users; a jealous capuchin monkey named Dr. Watson who helps Judy’s husband, BJ (Tim Baltz), recover from a pole dancing accident; and a water skiing scene with Goggins that doesn’t feature any clothing.

And without getting into details, look for an elaborate set piece with Baby Billy singing a Christian-themed pop-rap tune that Goggins jokes “should become the song of the summer.”

Where McBride was front and center in both of his previous series, “Gemstones” is an ensemble effort that often features the three Gemstone kids in lightning-fast crude exchanges. They seem totally improvised, and yet they’re not.

“It’s one of the most scripted shows I’ve done because otherwise the scenes could go on forever,” says McBride, who allows that room was left for a few alternate takes in case magic was in the air.

Goggins says that if anything, he is to blame for many ruined takes. “Those three, they’re just such pros at improvisation, they keep it together, but I’m the one person who can’t hold it in, to the point where people would get pissed off about it,” Goggins says. “They all can make you laugh just as easily as they can break your heart.”

Why Danny McBride hid Season 4 was the last from the ‘Righteous Gemstones’ cast during shooting

The Gemstone story arc is by no means complete by the final episode. It feels like there still is more road to this journey. The cast presumed as much, too, as they shot the entire season in and around McBride’s hometown of Charleston, South Carolina, assuming a Season 5 would be happening.

“My personality is, ‘Hey, this is so great, let’s do 20 seasons of it, guys,’” says Patterson, who is also a writer on the show. “But Danny always has a more balanced approach, and his feeling was, ‘Let’s go out on a high.’”

Freeman says McBride didn’t want his cast weepy and mopey and “being heavy while playing the last season, which was smart.” But that led to a rather startling moment on the very last day of filming.

“We were shooting a group scene with the monkey, and it was 3 a.m. and Danny was directing and then he started in on this speech,” Freeman says. He was announcing that this would conclude the series.

“Everyone started bawling,” she says. “We stayed for two hours, just hugging and talking and saying how much we appreciated each other.”

McBride says he loves his cast and crew, and “it would be easy to do another five seasons of this.” But he adds that he wrote the pilot eight years ago, and the four seasons were shot over six years because of COVID-19 shutdowns and Hollywood strikes. Even this season had its challenges, which included everything from Goggins’ double duty on the new season of “White Lotus” to a hurricane that threatened to upend a few key final scenes.

Mostly, though, it was time to move on.

“If I’d just kept making ‘Eastbound & Down,’ who knows if I’d have done ‘Vice Principals’ and so on?” McBride says. “I was just trying to find that balance, giving something its due but not being afraid to come up with what’s next.”

What’s next is for future discussions. For now, we’ve all got another two months of one of the most hilariously outrageous families ever seen on television, so it’s time to sit back and enjoy the glorious train wreck that, in the end, has an unmistakable beauty to it.

“I knew coming into this season I really wanted to push it,” McBride says. “But I also knew that the trick with ‘Gemstones’ is, you can take it to outer space, but there has to be enough heart in it so that you can still land the ship on planet Earth.”

Mission accomplished.