This verse, as well the last sentence of the previous verse, is not found in the Marcan parallel. Both Revised Standard Version and Good News Translation represent a fairly literal rendering of the Greek text.

Some translators will find that they need to make the connection between John and Elijah quite explicit: “Then the disciples understood that in speaking to them about Elijah, Jesus was really speaking about John the Baptist.”

Quoted with permission from Newman, Barclay M. and Stine, Philip C. A Handbook on the Gospel of Matthew. (UBS Handbook Series). New York: UBS, 1988. For this and other handbooks for translators see here .