Her father

Neither John nor Sherlock thought to ask the young girl her last name. It wasn't any of their business. Sherlock's daughter was happy. More than that. Ellie Holmes was in love with Arrabella, that was all that mattered.
Bella's father was similar to Sherlock in that he didn't seem it necessary to ask Ellie's last name.

Both Ellie and Bella had planned for such a thing. Neither one wanted to admit who exactly they had fallen in love with.