The other biological parent of Celestia’s triplets, Captain Eclipse! They’re the current captain of Celestia’s personal guard, and the princess trusts them more than she trusts most. They’re a bit intense and brash, as you’d expect from a captain, but at the end of the day they’re down-to-earth and always willing to do what needs to be done. When she was looking for a suitable sire for her children, Eclipse was among Celestia’s first choices. She was a bit wary of asking, for fear of making things awkward between them, but Eclipse was happy to help. It probably didn’t hurt that they had a huge crush on the princess and probably would’ve done anything she asked, but. Y’know.
Eclipse has a pretty good relationship with the triplets, but they don’t see them all that much. Royal guard-ing is a full time job!