Dean (Ackles) and Castiel (Misha Collins) appeared to overcome their rivalry in recent episode, 'The Born-Again Identity'.
However, according to Zap2it, both actors admitted at a recent convention in Rome that they had struggled with parts of the episode, which they considered "unmanly".
"There was a certain line that we couldn't get past, it was so out of character and horrible," Ackles explained.
Collins agreed: "There was stuff that was written in that [reunion scene] that was really tough to say."
Ackles joked that Supernatural showrunner and writer Sera Gamble had given their characters such emotional dialogue because "she's a girl".
"We proceeded to spend the next hour and a half trying to figure it out," he continued. "The three of us tried to put our minds together on set to say, 'How can we change this around to make it more believable between these two characters?'."
Collins will reprise his role as Castiel once more in this week's Supernatural episode 'Reading is Fundamental'.
The series continues on Fridays at 9/8c on The CW.