For years, Bob Harper and Jillian Michaels appeared to have great chemistry onscreen while filming "The Biggest Loser" together. But a new docuseries about the NBC weight-loss competition has fans wondering if the dynamic duo actually got along in real life.

Harper is practically synonymous with The Biggest Loser. He trained contestants for the first 16 seasons and hosted the final two of the show’s 18-season run. Between seasons 17 and 18, Harper suffered a heart attack that left him unconscious for two days in February 2017.