The Friend — the new dog-centric film from Bleecker Street Films that opens in theaters nationwide on April 4 — doesn’t specify which of its characters is reflected in the title.

But since there’s a dog in the credits, do we really need to tell you?

Based on the novel by Sigrid Nunez, The Friend kicks off with the untimely death of “Walter,” a curmudgeonly writer played by the ever-inscrutable Bill Murray. Despite having left behind three wives, Walter bequeaths his 150-pound Great Dane to his longtime friend and protégé Iris, played with appealingly nervous energy by Australian actress Naomi Watts.

To say Iris is ill prepared for her four-legged inheritance is an understatement: “Apollo” commandeers her bed, makes cotton candy out of her throw pillows, and balks at the elevator, requiring a five-story climb to her postage-stamp-sized apartment in a no-dogs-allowed building. Could the eviction notice be far behind?

As Iris processes her emotions — love, regret, anger, frustration and, above all, grief — The Friend becomes the story of another irreplaceable confidante: the imposing black-and-white dog (in real life, a Harlequin Dane from Iowa named Bing) who helps her tap into long-buried dreams and emotions.

That wordless bond between dog and human transcends time and place, whether you are tossing a tennis ball at the dog park or trotting across Westminster’s signature green carpet.

“They say man’s best friend,” mused Bill Murray in a private interview, with Bing lying regally at his feet sporting a signature purple Westminster collar and leash. “You know, sometimes it’s man’s only friend … There are times when there is no one else to turn to for any kind of solace, someone who’s not going to judge you — or bite you, literally.”

Bing, massive head resting on his equally huge paws, reserved comment.

Both the film’s stars have owned small mixed breeds — Murray’s now deceased Cairn- Russell mix, Timmy, once fended off a coyote, and Watts describes her current sofa sitter as a six-pound “Terrier meets Chihuahua” cross. So a dog of Bing’s stature took some getting used to for Watts — who he outweighs by dozens of pounds.

“It was daunting at first,” says the actress about the “lots of unpredictable things” they encountered filming in the streets of Manhattan, from horn-blaring traffic to other canine passersby. “People want to come up — he’s a rock star. Everyone’s blown away by his presence.”

As for Bing himself, the almost-seven-year-old seems unfazed by all the attention. His official name — that’s Ch. Flighty Foto White Christmas CD RA CA DCAT TKI CGC TT CHIC to you — is an aria of acronyms, reflecting titles in everything from dog shows (yup, he’s a champion) to obedience to trick training. Maybe that’s the key to Bing’s comfortable-in-his-own-skin success: Strive for balance in all things, and remember that it’s the moments that matter, not the medallions.

“I’ve had dogs all through my life, and I can’t imagine a life without a dog,” Watts said, holding the leash of a snoozing Bing. “I have long conversations with my dog. … And it’s not just ‘When’s the next piece of chicken coming?’ There’s a soulful look in their eyes that you just feel connected to.”

For the record, though, Bing would likely maintain that the arrival of a McNugget is always of keen interest. After all, even the best of friends have their priorities.