A Harvard University professor has unveiled a fourth-century fragment of papyrus she says is the only existing ancient text quoting Jesus explicitly referring to having a wife.

Karen King, an expert in the history of Christianity, on Tuesday said the text contains a dialogue in which Jesus refers to “my wife”, whom he identifies as Mary.

King says the fragment of Coptic script is a copy of a gospel, probably written in Greek in the second century.

King helped translate and unveiled the tiny fragment at a conference of Coptic experts in Rome.

She said it doesn’t prove Jesus was married but speaks to issues of family and marriage that faced Christians.

Four words in the 3.8-by-7.6-cm fragment provide the first evidence that some early Christians believed Jesus had been married, King said.

Those words, written in a language of ancient Egyptian Christians, translate to “Jesus said to them, ‘my wife’,” King said in a statement.

In the dialogue the disciples discuss whether Mary is worthy and Jesus says “she can be my disciple”.

Christian tradition has long held that Jesus was unmarried even though there was no reliable historical evidence to support that, King said.

The new gospel, she said, “tells us that the whole question only came up as part of vociferous debates about sexuality and marriage”.

“From the very beginning, Christians disagreed about whether it was better not to marry,” she said, “but it was over a century after Jesus’s death before they began appealing to Jesus’s marital status to support their positions”.

King presented the document at a six-day conference being held at Rome’s La Sapienza University and at the Augustinianum institute of the Pontifical Lateran University.

The fragment belongs to an anonymous private collector. Nothing is known about the circumstances of its discovery, but it had to have come from Egypt.