A single Lupita Nyong'o, who a source confirms has split from her rapper boyfriend K'naan, was "flirty" with her fellow Oscar winner Jared Leto at a SAGs afterparty on Sunday, Jan. 25 -- get the scoop here. Credit: Stefanie Keenan/WireImage

Could Jupita be a thing?! Lupita Nyong'o and Jared Leto, the sexiest fake couple at the 2015 SAG Awards, attended an afterparty at Sunset Tower in West Hollywood on Sunday, Jan. 25, where they were spotted getting "very flirty," an observer tells Us Weekly.

Meanwhile, another source confirms to Us that Nyong'o is single after splitting from her rapper boyfriend K'naan.

The insider close to Nyong'o tells Us that the 12 Years a Slave actress was the one to break off her relationship from K'naan. Their split happened last year, the source adds.

Meanwhile, the eyewitness at the Meiomi Wines-sponsored bash tells Us that Leto was making moves and "majorly flirting" with the Brooklyn beauty. Earlier that evening, last year's Oscar winners for Best Supporting Actress, 31, and Actor, 43, both presented onstage at the 21st Annual SAGs, where their chemistry was palpable -- so much that it sparked reaction from social media fans.

The party observer adds that the Dallas Buyers Club actor "was a whirlwind" at the West Hollywood hotspot. "He came in and spoke to Harvey [Weinstein] for a second, than raced right for Lupita," the insider tells Us. "He hugged her and started whispering to her quietly."

The unattached actress was receptive to Leto's attention, following his lead as he "dragged her right to the dance floor."

While dancing, the stars "were whispering and laughing" closely together. "At one point they were sticking their tongues out at each other and staring into each other's eyes," the observer adds to Us. "It was very flirty. Then Jared said he had to go but he told her to text him later and he ran off.”

Nyong'o and Leto's flirtatious ways are nothing new. The two swept the stage at the MTV Movie Awards last April, a month after their big Oscar wins, and subsequently dodged dating rumors at Paris Fashion Week.

Us Weekly exclusively revealed last March that Nyong'o was dating K'naan. Leto, meanwhile, was previously linked to Miley Cyrus briefly last February, after a source revealed to Us that they were "hooking up."