Barnaby Edwards (in-universe)

Barnaby Edwards was a companion of the Doctor sometime after his tenth incarnation.

Biography
Barnaby travelled with the Doctor for some time before leaving him after he fell in love. The Doctor entrusted him with a message for his former self. Barnaby encountered the Doctor again on his birthday while living in a care home. Barnaby was unaware that this was an incarnation of the Doctor who was yet to meet him. He gave him the message and then died. (IDW: Old Friend)