[Warning: The following contains spoilers for the Season 5 finale of Legends of Tomorrow. Read at your own risk!]

In a bizarre fight sequence during DC's Legends of Tomorrow's Season 5 finale, titled "Swan Thong," the gang battles an army of reanimated Encores, like Courtney Ford's Marie Antoinette, while Sisqo delivers a full-on performance of the "Thong Song" in the background. If that sentence has you scratching your head and wondering what the heck you just read, imagine having to explain that odd but fun chain of events — which also includes Nate (Nick Zano) using one of Sisqo's moves as an offensive tactic — to the man behind the hit single.  

"When I called him, my heart was beating so fast. I was trying to sound cool and not too desperate — but I was desperate," co-showrunner Phil Klemmer says of his terrifying phone call to the singer-songwriter.

Legends was four days away from filming the finale and Klemmer hadn't yet secured the silver-haired, dragon mic‑wielding performer for an appearance, which he worried wasn't going to be an easy sell. After all, the episode required Sisqo to stand in an exhibit dedicated to his chart-topping single "Thong Song," which was featured in the Fates' Hall of Bad Ideas alongside other creations like the Shake Weight, glitter, and cigarettes. The difficult part was explaining that the episode wasn't so much dissing the "Thong Song" as it was celebrating the 2000 summer anthem — all while getting the famed singer to understand the premise of the zany CW series.  

"The words coming out of my mouth just sounded like nonsense because I had to explain five seasons of our ludicrous show," Klemmer said. "I really expected him to be like, 'No thanks, click!' But he was just so gracious, so on board, and came to play."  

Sisqo, <em>DC Legend's of Tomorrow</em>Sisqo, DC Legend's of Tomorrow

Not only did Sisqo turn up on set fully costumed and with his hair dyed, but the flamboyant entertainer also brought his signature dragon microphone and a face that hasn't aged in 20 years. But in true Legends fashion, Sisqo's unexpected appearance was just the tip of the iceberg. The hour also featured a stellar rock performance by Charlie (Maisie Richardson-Sellers), who won't be returning for Season 6, and Sara (Caity Lotz) being swept up by a mysterious blue light. While we don't yet know why she's been kidnapped, Klemmer revealed what Sara and the rest of the Legends will be dealing with next season.   

"She has been taken by space aliens, and they had a very particular design on Sara Lance," he explained. "She's just not your average Jane on the street. She's in for a gnarly ride, but more importantly, the Legends are in for a gnarly ride because they have really grown to rely on her — especially Ava. It's going to be, as always, a mashup of some very silly, goofy genres and some hopefully powerful, personal, emotional stories next season."

One of those personal stories will include Nate working past yet another heartbreak after Old Zari (Tala Ashe) decided to return to the totem in order to save her brother Behrad (Shayan Sobhian). It's the latest in a long list of heartaches that also includes Amaya (Richardson-Sellers), who was forced to return to her village, and his best friend Ray Palmer (Brandon Routhleaving to start a new life with Nora Darhk (Ford).

"I don't know why we keep breaking Nate's heart," Klemmer said. "I guess there is something sadistic about taking a handsome fellow like Nick Zano and just making him the most unfortunate fool. I think he maybe will have learned his lesson [next season]… I think he's probably just given up [on romantic relationships]. He needs to pursue some platonic relationships."

Nate might be putting his love life on pause in Season 6, but it looks like Zari and Constantine (Matt Ryan) will be forging ahead as a couple when the series returns with new episodes. But putting two strong-willed characters together is a lot easier said than done. Despite their undeniable chemistry on screen, Klemmer admits that writing their relationship has been extremely difficult and has left the writers' room almost divided.  

"It's really hard to break stories because when you have them fight, who's supposed to win? We talk ourselves into circles," Klemmer added. "We as the writers are actually having a fight with them as our avatars, and everybody will choose their avatar and they'll be like, 'No, John looks weak. That can't happen.' It's like, 'No, Zari comes out looking weak.' 'Well, John's not going to change.' 'Well, Zari's not going to change.' This goes on for hours and days and you're like, 'Oh my God, I feel like I'm in a relationship. I feel like I'm in a toxic relationship, but I can't get out of it because it's so alluring.' We're basically, as a [writers'] room, living their romance. It's the best thing and it's tearing us apart."

Seasons 1-4 of Legends of Tomorrow are currently streaming on Netflix. Season 5 will be available on Wednesday, June 10. 

Caity Lotz, Matt Ryan, Olivia Swan, Dominic Purcell and Nick Zano, <em>DC Legends of Tomorrow </em>Caity Lotz, Matt Ryan, Olivia Swan, Dominic Purcell and Nick Zano, DC Legends of Tomorrow