Blake Lively was Penn Badgley's "worst" screen kiss.
The 28-year-old actor enjoyed locking lips on screen with his 'Gossip Girl' co-star when they were dating, but admits things were awkward once they had ended their relationship in 2010.
He said: "I'll say Blake [was the best on-screen kiss] because we actually had a relationship at the time.
"And worst? Maybe Blake after we broke up."
However, Penn thinks he and Blake - who has a two-month-old daughter with husband Ryan Reynolds - deserve credit for how they conducted themselves at work after they split.
Speaking on 'Watch What Happens Live', he said: "We were actually consummately professional, to be honest.
"I think we should both pat ourselves on the back for getting through it -- because, you know, anything is complicated in that way, and we handled it."
Penn's character Dan Humphrey was unmasked as the person behind Gossip Girl at the end of the series, and he thinks the revelation shows just how complex his alter ego was.
He mused: "I think it was probably the most plausible.
"It makes him a bipolar, transgender schizophrenic, like obsessive-compulsive, incredible manager of time. You know?"