"Nick will sleep with any girl who gives him attention," an insider told Life & Style. "Nick definitely sleeps with his three finalists and one other girl, and there are probably at least a few more."
After developing a reputation as a sexually-charged villain on The Bachelorette's tenth and eleventh seasons -- although he redeemed himself with a slow-moving romance on Season 3 of Bachelor in Paradise -- the bachelorettes reportedly prepped themselves for intimacy going into Season 21 of The Bachelor.
"Many of the new girls this season came in the house knowing that sex is important to Nick, and were completely onboard with the idea," the source said. "It definitely gets steamy in the Bachelor mansion, and the cameras weren't always rolling."
From a viewer's perspective, every Bachelor is afforded three overnight Fantasy Suite dates away from cameras.
"What viewers don't know is that Nick has a chance to spend more time with several of the ladies than you see on TV," the source explained.
"No one truly knows how many people Nick slept with during his Bachelor run. But he definitely tried to make moves on every single girl. Some of the women went to first base, some second base and others hit a home run."
In the months leading up to his The Bachelor role, Viall was reportedly playing the field heavily.
"Just before leaving for the show, he was sleeping with girls all the time," the insider told Life & Style, "and most of the girls he hooks up with are part of the Bachelor Nation, because that's who he hangs out with."
Going back even further into Viall's dating history, he engaged in a romance with Jennifer Saviano on Season 3 of Bachelor in Paradise in Summer 2016. And before that, he slept with Bachelorette Kaitlyn Bristowe mid-season during a one-on-one date in Ireland.
"He told me that they had sex all of the time [on the show]," revealed Viall's friend Abby Draper. "Any time they were together, it was mostly physical."
Viall almost memorably publicly revealed on national television he had slept with Andi Dorfman onThe Bachelorette the season prior. Dorfman called the disclosure "below the belt," especially since she ended up engaged to a different man, Josh Murray.
Viall's The Bachelor winner "is already not happy about how much of a pig Nick has been," the source insisted. "Nick has slept with a good chunk of the contestants but she fell in love with him for other reasons."
"That's my man Bob Guiney! I think [his number] was five and half," Fleiss said during ABC's Inside The Bachelor: The Secrets Behind the Rose 20/20 special in 2010.
"Bob had just come off the Trista season of The Bachelorette so his popularity was enormous. I think the women, they were in love with him from the start. I love you Bob!," said Fleiss, explain how Guiney had appeared as one of Trista Sutter's The Bachelorette first-season suitors before his The Bachelor edition.