Definition: In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].
Input: When Bobby and Riley George were born 30 minutes apart with light skin, curly hair and brown eyes there was no doubting they were twins. But four years on, the boys couldn't be different as Bobby has blue eyes and a light complexion while Riley's skin and hair is dark like his father's. The twins, from Feltham, West London, were born to mother Abigail Tongue, 22, who is white and father Richard George, 26, who is of mixed race. When they first found out that Miss Tongue was expecting twins, doctors said there was a one-in-a-million chance that the babies, created by two separate eggs, would have a different skin tone.Twins Bobby and Riley George were born in 2011 and looked similarTheir mother Abigail is white and their father Richard is of mixed raceBut at six weeks old both boys' appearances started to change differentlyBobby now has light skin and blue eyes and Riley brown eyes and dark skin 
 Question:At the same time _'s skin started to become darker and his hair became straight and brown.

Riley George