The boy claimed he saw the girl performing oral sex on the now 14-year-old. He also said he recorded a 10-second video which showed the girl performing oral sex on him whilst the now 16-year-old boy was behind her.
"Did you know what [the now 16-year-old] was doing?" Mr Gilmour asked. "He was having sex with her," the boy said. The now 15-year-old said he had told the girl to 's* it'.
Asked why he decided to film the encounter, he said: "Because at the time I used to film everything I did. I thought it was OK to film her."
Asked if he thought what he was doing was wrong, he said no. He said he sent the video to the now 16-year-old 'because he asked him to'.
Asked why he left the bush, he said: "I left because I wasn't h**d and I couldn't do anything and my mates were going. I just followed them," he said.
When questioned why he ran from the bushes, he said: "You can see us running around town all day, that's what we were doing."
Mr Gilmour asked how he felt about the incident. he said: "It doesn't make me feel very good, that these people are saying these false allegations. And my family have gone through a lot of stress about it. It's just not been nice seeing my family stressed."
He added: "I don't feel very happy about what happened."
The boy previously told the court that he left school early and worked for his family's business.
The trial has previously been told how the boys "took it in turns and swapped positions" during the incident in February 2024.
Prosecutors say part of the alleged attack on the then-13-year-old was filmed on a mobile phone and was later "circulated amongst themselves" and "others".
Previously, Ms Whittlestone said the now 14-year-old has been found unfit to stand trial.
She said the jury would be asked to find "whether he did the act" and whether he "encouraged" it to happen without the girl's consent.
The indictment contains five counts of rape. Three counts relate specifically to each boy, while two are charged as 'joint enterprise', jurors were told. Each boy denies the charges they face.
The trial continues. This was from previous reporting of trial