For the boy was allegedly incited to have sex with a 31-year-old woman – while a group of adult men filmed them.
The unsavoury saga of the swingers in west Wales was described to Swansea Crown Court.
The jury heard how the boy had been taken by his mother to the home of family friend Iwan Walker, 24, who had invited him to spend the night.
Prosecutor James Jenkins said Walker knew the boy and 'knew full well how old he was'.
He said Walker had phoned Brian Ecclestone, 32, and then told the boy they were going to visit some of his friends.
Ecclestone, 32, arrived in his car and drove Walker and the boy to his home in Llandysul.
Once there, the boy was incited to have sex with Ecclestone's partner, Emmanie Hughes, 31.
"He was not the only one. It would appear that all the defendants had sex with her or at least were actively watching and encouraging each other," said Mr Jenkins.
"There is no doubt this group sex took place, and that the boy was part of it with the active encouragement and excitement of the defendants."
The boy later told police that he had felt pushed into having sex with Hughes, who had performed a sex act on him before the pair had sex together.
He told the jury: "Bryan told me to go upstairs with her. I felt really pressured. She lay on the bed and started playing with me.
"Bryan walked in and said I was doing a good job. Walker came into the bedroom while I was with her."
The next day, the boy was collected by his mother 'and she thought he did not seem himself'.
After the boy confided in a friend, his mother was informed and the police were called and the men and woman were arrested.
Hughes told police that she accepted having sex with the boy but thought he was 16. She described the 13-year-old as 'muscular and confident', and said he appeared to know what he was doing.
"I thought he was older, he told me he was 16," she told the court.
"I had no reason to doubt what he said. He initiated sex; he was the first to ask me to go upstairs. Bryan came afterwards to see if he was ok."
And she told police during interview: "I am not in the habit of asking for ID."
She added: "Brian filmed. He (the boy) filmed as well."
She said she later had sex with Sweetman and Walker.
Ecclestone told the jury he and Hughes had been swinging since 2010.
He said the boy told him he found Hughes attractive and asked if he could lose his virginity with her.
"It made me feel good that someone else found my partner attractive. I was happy for them to have sex," he said. "She found it quite flattering, to be honest."
Hughes and Ecclestone, both of Llandysul, Sweetman, of Newcastle Emlyn, and Walker, of Saron, all deny inciting a child under 16 to engage in sexual activity with Hughes.
Hughes denies a further charge of sexual activity with a child. The trial continues.
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