Mombasa was part of the state of Zanzibar until 12 December 1963 when it was ceded to be incorporated into the newly independent state of Kenya.
Yes, I’ve read that at several other threads here at FR.
You wrote-
“Mombasa was part of the state of Zanzibar until 12 December 1963 when it was ceded to be incorporated into the newly independent state of Kenya.”