Note: This is not really my type of story. It goes against my convictions about Spock and who his children might or might not have been. I would not have written this if it had not come to me in a dream last night and demanded to be written.
When he was invited to the ceremony, Nogura looked curiously at Kirk and Spock. "A Vulcan ritual for the birth of your granddaughter?" he asked.
"Yes, for the birth of our granddaughter," the human and Vulcan replied, smiling at each other.
"A granddaughter belonging to both of you?"
"Indeed," they insisted. "This granddaughter is both of ours."
"Most interesting," said the admiral. "I didn't even know you two were married."
"We are not married," said Kirk and Spock. "Look more closely at the invitation."
Nogura did, and saw the words, "For the Birth of the Daughter of Saavik and David."