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As part of NCIS: LA's upcoming episode in which the stars' mothers make a cameo, ET had the chance to catch up with LL Cool J and his mother on the set and found out when she knew that her son was destined to be a star.

Cool J's mother, Ondrea, revealed that that moment for her was when her now-actor-and-rapper son slipped away from his grandmother when he had tagged along with her shopping at a young age.

VIDEO: Cool J Teases 'Shocking Surprise' on 'NCIS: LA'

"She said he was around the corner saying the ABC's like Shakespeare with a whole crowd around him," she recalled. "That's when I said, 'I guess he's going to be performing.'"

His mother will appear on tonight's episode of NCIS: LA alongside the mothers of Chris O'Donnell, Eric Christian Olsen, and Daniela Ruah. The mothers' cameos stemmed from a proposition that the executive producer made at a party to have them on the show.

Cool J, born "James Todd Smith," revealed that his mother's acting skills were much better than he had expected, and was happy that she was able to be on the show with him and see how the production operates.

VIDEO: Behind-the-Scenes Look at 'NCIS: LA' Explosions

"She did excellent. She did better than I thought she would do," he said. "I was nervous. I thought she was [going to say], 'What do I do, Todd? What do I do?'"

Check out the full video above to hear the other moms reveal when they knew their children were going to be stars. The full episode of NCIS: LA will air tonight at 9 p.m. on CBS.