Lim Yi Sheng wanted to tell Samantha first about her identity before letting their grandfather know about this because he can't exactly predict what reaction he might have once he dropped this news.
His father having illegitimate children might even give him a heart attack, when his older uncle got another woman pregnant despite already having fiancee his grandfather went ballistic.
Their grandfather, Lim Ming Cong might not look like it but he is a difficult character to handle, his strong personality towards the men in the family and his hatred for failures would automatically snap when the button was pressed.
He also deeply values family more than anything else that is why Lim Yi Sheng has always been reluctant up to now.
Furthermore, there is also his mother and Shinyi that he has to consider. Just what would his mother feel if she knew that her husband had a child with another woman when Shinyi was only four years old back then.
