Sweeney hosted "Saturday Night Live" this week, and during her opening monologue, she addressed all the talk about her supposed romance with Powell in Australia during the 2023 shoot for their rom-com, "Anyone But You."

Sweeney told the SNL audience the "craziest rumor" about her was that she had this affair with Powell, pointing out, "That's obviously not true" ... declaring her fiancé, Jonathan Davino, produced the film, and, as such, was there with her during filming.

Then she set up a gag, saying her Jonathan was there in the 'SNL' studio to support her -- but when the camera cut to him ... you-know-who was sitting in the studio.

The monologue was just the first time Glen would appear on camera ... he also made a cameo later in the show, as Sydney's boss -- with whom she was cheating.

Clearly, the 'SNL' writers found Sydney and Glen's alleged romance interesting enough to lean on it throughout the show -- and good on GP for playing along and showing up in-studio for the jokes.

However, Syd's real-life guy, the long-suffering Davino, was actually in the studio all night ... he just remained behind the scenes.

Jonathan was right by Sydney's side, though, when they strolled into the 'SNL' afterparty. The couple held hands as they entered. Musical act for the night, Kacey Musgraves was also there, along with Glen and other cast members.

For the record, the "Euphoria" actress got engaged in 2022 to Davino -- a restaurateur -- after the couple dated for about 4 years.

But, while Sweeney was on the "Anyone" set, she looked very cozy with Powell in paparazzi photos taken on the beach in Australia, sparking the chatter about their alleged affair.

The pair also posed together at CinemaCon in Las Vegas, staring deeply into each other's eyes.