John Irving was actually born with the name John Blunt, and was later
changed to Irving when his mother remarried.
The Dictionary of Literary Biography offers additional details:
"...John Irving was born in Exeter, New Hampshire, on 2 March 1942.
His birth name was John Wallace Blunt Jr., in honor of his biological
father, a World War II flyer who was shot down over Burma. Irving's
mother, Frances Winslow Irving, legally changed his name to John
Winslow Irving when he was six years old after he had been adopted by
her second husband, Colin F. N. Irving..."
Another take on the story is provided by the Wikipedia entry on John Irving:
"...John Irving was born John Wallace Blunt, Jr. in Exeter, New
Hampshire. His mother Helen, a descendant of the Winslows, one of New
England's oldest and most distinguished families, divorced Irving's
biological father, an airman serving in the pacific, when Irving was
two years old. The family maintained a strict silence regarding his
natural father. When her son was six years old, Helen Winslow married
Colin F.N. Irving, a Russian History teacher at the prestigious
Phillips Exeter Academy. John Wallace Blunt, Jr. was adopted by Colin
Irving and became John Winslow Irving in name..."
I trust that fully answers your question. But if there's anything
else you need, just let me know by posting a Request for
search strategy -- Searched Google and several biographical databases
under the author's name.