Carolyn Bessette-Kennedy's sapphire engagement ring was inspired by Jackie Onassis

The fifth episode, "Battery Park," zeroes in on a specific piece of her wardrobe: Her engagement ring.

John F. Kennedy Jr., played by Paul Kelly Anthony, proposes while the two are on an intense weekend with the entire Kennedy clan. Carolyn is unable to say yes due to various concerns, which the episode unpacks.

But she does keep coming back to the ring.

According to Elizabeth Beller, author of the Bessette biography "Once Upon a Time," the ring tied together both Kennedy's family history and Bessette's style.

Carolyn Bessette and JFK Jr, with her ring on display. (Robin Platzer / Getty Images)

Kennedy modeled the ring off of what his mother, Jacqueline Kennedy Onassis, called her “swimming ring”: “pared down and elegant, perfect for swimming.” (Her first engagement ring was a combined five carats of diamonds and emeralds.)

Kennedy Onassis’ ring was made with emerald and diamonds and set in gold, whereas Bessette’s was platinum with sapphires and diamonds.

Jacqueline Kennedy Onassis wearing her "swimming ring" in Hawaii in 1966. (Bettmann / Bettmann Archive)

The ring “was perfect for Carolyn and her understated (elegance)” Beller writes. The fashion executive rarely wore jewelry and was known for her simple, classic looks.

Bessette never met Kennedy’s mother, who died of cancer in 1994.

This was a point of contention for the couple, who met in 1993. Beller quoted an anonymous friend of Bessette’s who said Bessette broke up with Kennedy “a couple of times” because he wouldn’t introduce her to his mother. Once, at Keens Steakhouse, “John rushed Carolyn out a side door when he spied Jackie across the room with her companion.”

Beller quotes Kennedy’s friend Billy Way, who said Kennedy “regretted” never introducing Bessette to his mother and pointed out their similarities — both children of divorced parents, both Catholic and both with a minimalist sense of style.

Bessette and Kennedy were married in 1995 in a small, secret ceremony on Cumberland Island in Georgia.

Speaking to TODAY.com, jeweler Page Neal, co-founder of Bario Neal, calls Bessette’s ring a “study in intentional simplicity.”

“At a time when engagement rings often centered on display and visibility, hers reflected a more personal and quietly confident point of view. Its restraint is precisely what gives it lasting power,” Neal said.

The ring, Neal says, fits into Bessette’s minimal, refined and “deeply assured” style.

“She favored clean lines and understated silhouettes, outfits that never feel overworked. This ring mirrors that sensibility. An eternity band sits close to the hand so that it becomes part of the wearer, rather than something that announces itself. That subtle integration is what makes it feel so aligned with her style,” Neal says.

Unlike many modern engagement rings, this was an eternity band, meaning there was no significant center stone (usually a diamond). The idea of a “swimming ring” suggests a piece “meant to be lived in, not taken off at the first sign of activity.”

“A ring like Carolyn’s doesn’t depend on scale to feel meaningful. Its appeal is rooted in proportion, personal expression and wearability,” Neal says.