Alice is throwing a party. She invites Bob to come to the party, and says he may bring another person with him. Bob arrives at the party accompanied by Carol. We could say Carol is Bob's guest.
What's the reverse of this relationship? Bob is Carol's _______.
Usually host is the reverse of guest, but that doesn't seem to fit here. As Alice is throwing the party, Carol's host would seem to refer to Alice, not Bob.
Escort could work but sounds overly formal, and moreover it seems to me that it carries connotations about Bob's relationship to Carol.
If possible, the term should:
be gender-neutral (so that it also works if Doris arrives accompanied by Edward, or Frances arrives accompanied by Glinda)
not carry connotations about any relationship between Bob and Carol (e.g. it should not imply that they are friends, spouses, in a romantic relationship, etc.)
make it clear that Bob, not Carol, is the person originally invited by Alice.