Duchess has a slight resemblance to Sunburst’s lost sister, Sunset Shimmer. This both brings back great memories he once had of them both as kids, and brings him a heart wrenching sadness that he tries to hide from his daughter.
 
Sunset shimmer, although running away to the human world, was pronounced lost by her family and authorities. Without the knowledge of where sunset truly is, Sunburst immensely misses his sister and tries his best to live on with his life despite his lost family member.
 
Though, he can’t help but feel that same nostalgic feeling whenever he plays with his daughter like he used to with his sister.