The Oscar winning pair — whose exact relationship is the subject of speculation — were both invited by the Italian designer to attend her plastic-wrapped fall-winter Miu Miu show in Paris.
And if that wasn't enough attention-grabbing, Nyong'o had to move seats in order to fit a tardy Rihanna in a fur leather jacket in the Miu Miu front row.
Meanwhile, former Balenciaga designer Nicolas Ghesquiere gave an admirable debut at Louis Vuitton attended by Princess Charlene of Monaco, Catherine Deneuve and Charlotte Gainsbourg.
But the ghost of Marc Jacobs' Louis Vuitton past lurked.
Here are details about the last day of the ready-to-wear shows.
LUPITA NYONG'O AND JARED LETO ATTEND PRADA'S MIU MIU SHOW
Even before Jared Leto thanked "my future ex-wife Lupita" in a speech at the Independent Spirit Awards on Saturday, there's been speculation that he and fellow supporting role Oscar winner Lupita Nyong'o have been an item.
The "12 Years a Slave" actress has laughed it off — most notably on The Ellen Show — but has not denied it.
Now, to further fan the flames, both stars were at Paris' Miu Miu show at the same time — and both nursing jet lag.
Nyong'o, who said she "really liked the show," looked radiant in a clean Miu Miu jacket with an off-white sparkling embroidered collar.
But Leto wore shades and admitted he was exhausted.
"But it's the best kind of tired you could ever imagine," he said, avoiding comment on the relationship rumours.
MIU MIU'S SPORTY PLASTIC WRAP
With a pinch of irony, Senora Prada wrapped the entire show venue — Paris' Environmental Council — in non-biodegradable plastic.
It was full of young, fun and colorful suggestions on how to keep warm and dry during fall and winter.
See-through pale blue PVC skirts came alongside a bright yellow raincoat with sporty tassels.
Or waterproof sheer red hooker boots that somehow remained classy were mixed up with skiing shades and quilted pastel ski jackets.
Not all the looks worked, but there were some great black and white fur maxi coats.
Besides, you have to admire this iconic designer's talent. Who else could mix a classic pale yellow pleated silk skirt 1950s with a multicolored see-through anorak and still make it work?
LOUIS VUITTON DEBUT
With a soundtrack featuring cat "meows" and lyrics such as "my fangs are sharp like barbs," was Ghesquiere second-guessing reactions to his show?
As it happens there shouldn't be too many claws out since the former Balenciaga designer did quite well.
It was a saleable collection, but his debut at Louis Vuitton was by no means a triumph.
After a start that felt a little undeveloped, or lacking in energy, the 42-year-old found his voice in a great series of sometimes sparkling miniskirt silhouettes channeling the end of the Sixties or the early Seventies.
It's a style one fashion editor described as neo-Mod: A-line minis, a cinched waist with leather belt and strap pointing down like a tie, alongside a V-shaped 70s collar.
This muse produced the best look: a sexy, clean-looking navy and black mini dress with blue suede panels on the bust and riding boots.
A strange feeling pervaded the understated show — perhaps it was because the memory of Marc Jacobs' theatrical fashion spectacles was still very much on peoples' minds.
After all, Jacobs spent 16 years at the house, and his shows are — quite literally — a hard act to follow.
CHLOE SEVIGNY IS FRIENDS WITH GHESQUIERE
Indie actress and fashion darling Chloe Sevigny catches up with her old friend Ghesquiere every time she's in Paris, even if it's just by SMS.
She said she loved his debut Louis Vuitton show, a simple spectacle that featured giant shutters that opened up to let in natural light.
"It was pure artistry and effortless. He doesn't need all the pomp and ceremony. He can let the clothes do the talking," she told The Associated Press.
Under Marc Jacobs, Louis Vuitton's displays earned a reputation for being, along with Chanel's, the biggest and costliest in town.
HERMES SPELLS LUXURY
This show — a fusion of Persian styles with menswear — was one of the most sumptuous displays seen all season.
The first piece, a loose silky dove grey jacket with large, almost abstractly-shaped lapels, set the mood. This looseness was carried though in pants, skirts and lapels, all in beautiful earth hues, broken up by slimmer silhouettes that sometimes featured Persian or Mughal Indian decorative print.
Menswear jackets added the on-trend touch, to show that designer Christophe Lemaire also lives out of Hermes' luxuriant bubble.
A two-shade menswear look near the end beautifully towed the line between male-female and East-meets-West, in a huge fur coat paired with purple-brown Indian silken pyjamas.
Thomas Adamson can be followed at Twitter.com/ThomasAdamsonAP