King's character Lemon is dating George (Scott Porter), but the series premiere hinted that she had previously had an affair with Lavon (Cress Williams).
King has now confirmed that the pair had a secret relationship but told TV Guide that it is over.
"It was during a very vulnerable time when she thought her relationship with George was going to be done," she said. "As soon as he came back and said, 'I want to make this work', she said, 'OK'."
However, King confessed that Lemon may be better suited to Lavon than George.
"When you see Lemon and Lavon together, you see the real Lemon," she said. "Her vulnerability is all there. With George she has a mask on - she tries to be this perfect woman. I think she truly loves George, but I think she's in love with Lavon."
King also suggested that her rivalry with Zoe (Rachel Bilson) will continue throughout the season, saying: "The reason why they fight so much is because they're so similar. They're both stuck in their ways and they both think they're right.
"We're shooting episode nine and we just had one line of a breakthrough, and then immediately we close it back off."
Porter has previously teased that George will cause problems in his relationship with Lemon by spending time with Zoe.
Hart of Dixie airs on Mondays at 9/8c on The CW.
> Hart of Dixie: First impressions
Watch a trailer for the next episode of Hart of Dixie below: