The picture, showing Amelia in Halloween get-up, was posted to Twitter.
He captioned the picture: "Happy Halloween!! Love tonight's episode with my tv sis @pinkferg84 @chrisflanagan83 #April #Leo #halloween2019 #emmerdale."
Fans rushed to comment on the picture.
One tweeted: "Lovely photo of you both."
A second commented: "Happy Halloween, Harvey."
A third said: "Enjoyed - lovely photo of you both Harvey."
In the ITV soap, Harvey plays Leo, who is the half-brother of Amelia's character April.
The pair have often been seen on-screen together.
It turned out other children were picking on Leo at school and April didn't want him to be ignored at the birthday party.
Happy Halloween!! Love tonight's episode with my tv sis.
Recently Rhona was surprised when Graham Foster used sign language to communicate with her son.
It turned out Graham had a brother named Steven who had Down Syndrome.
Sadly Steven died at the age of 15 leaving Graham devastated.
In last night's episode of the soap (October 31 2019) Rhona and Graham's relationship was made public, but Marlon expressed his concern over Rhona being in a new relationship.
Emmerdale airs weeknights at 7pm on ITV, with an extra episode at 8pm on Thursdays.
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