Elisha Cuthbert stars in “One Big Happy”

It’s been 18 years since Ellen DeGeneres’ character came out of the closet in her sitcom “Ellen,” shortly after the actress herself came out to the public in the real world. The groundbreaking “The Puppy Episode” has been credited with being one of television’s most influential gay moments and with blazing a trail for LGBT-centered shows that followed, such as “Will and Grace,” “Modern Family,” “The L Word” and “Glee.”

Now, the comedian and much-loved talk show host is producing “One Big Happy,” a sitcom focused on a single lesbian and her male best friend who decide to have a baby together. The series kicks off Tuesday, March 17, on NBC.

Canadian-born beauty Elisha Cuthbert (“Happy Endings”) plays Lizzy, a young woman who, at 30, is ready to move into parenthood, despite being single. Luke (Nick Zano, “2 Broke Girls”) has been her best pal since childhood, and as kids, they both went through the difficulty of their parents' divorces. Neither is in a relationship but both want to start a family, so, since they’re practically family anyway, they decide to have a baby together.

It sounds like a great plan, until Luke meets stunning bartender Prudence (Kelly Brook, “Smallville”), who’s due to return to her native England in a couple of days. Instead, the two fall head over heels in love and embark on a whirlwind romance, and just when Lizzy finds out that a bun is officially in the oven, Luke and Prudence announce that they’ve tied the knot.

The co-parenting scenario was an unusual one to begin with, but now the three of them are, well, sort of a couple.

It’s not an all together unheard of state of affairs, though. In fact, the show is loosely based on creator Liz Feldman’s own life. Feldman, whose writing and producing credits include “2 Broke Girls” and “Hot in Cleveland,” was heavily influenced by DeGeneres’ coming out in 1997. She met the actress at a book signing the following year, and a friendship formed between the two women. Years later, DeGeneres even hired Feldman to write for “The Ellen DeGeneres Show.”

Like Lizzy, Feldman was all set to have a baby with her straight male best friend when he met the love of his life, derailing their plans.

“Honestly, it was so difficult to deal with it when it happened, the only thing I knew how to do was write something about it,” Feldman said at NBC’s Television Critics Association panel in January. “This comes from a real place. It’s not coming from any sort of agenda, what can we do to put another lesbian on that television. It’s coming from the truth.”

The showrunner also noted that Ellen’s coming out in 1997 is what made “One Big Happy” possible, but DeGeneres noted at the TCA panel that, while the female lead happens to be gay, that’s not what the show is really about.

Elisha Cuthbert and Nick Zano as seen in “One Big Happy”

“Yes, there’s a lesbian character, but it’s a really funny show and that’s all I wanted to do: put out funny material and thought-provoking material,” adding that she didn’t set out to create a “groundbreaking” show and doesn’t seek out gay-specific material for her production company.

In fact, Lizzy is really the only gay character in the show. An ex of hers will appear in one of the early episodes, but, according to DeGeneres, the character is too difficult and dysfunctional at this point to be able to handle a romantic relationship.

The main question is one that many single men and women in their late 20s and early 30s are facing, perhaps more so today than ever before: what do you do when you’ve reached the point in your life where you want to have children but haven’t met the person you want to spend the rest of your life with?

In past decades, 30 was considered spinsterhood for an unmarried woman. These days, men and women alike are waiting longer to get married, refusing to settle for someone not quite perfect just because he or she came along at “the right time.” Unfortunately, our biology hasn’t clued in to the fact that we’re no longer dying off at 40 and therefore might not want to start churning out babies before we hit 20. If parenthood’s on the table, most people want to get cracking before they hit their mid-30s.

What Lizzy and Luke have worked out is really the perfect solution -- until a Prudence enters the equation. Far more important than Lizzy's sexuality is the situation in which she's suddenly found herself: she's going to have a baby with a man who's married to someone else.

Despite “The Puppy Episode” being “Ellen’s” highest-rated episode and the buzz it stirred, the show also received a good deal of backlash and was canceled the following season. A lot has changed in the past 18 years, though, and there have been enough wildly successful shows that have featured prominent gay storylines to help usher in a new era of acceptance. As Feldman said at the TCA panel, “I think what we’re trying to do is almost pick up where [Ellen] left off in a way, except it’s 18 years later, so I think the world is ready for it on a new level.”

Catch the season premiere of “One Big Happy” when it airs Tuesday, March 17, on NBC.