The actor and his wife Michelle Edwards welcomed their first daughter Arrabella last month. Speaking to Hello magazine, McDermott - Ryan Malloy in the BBC soap - praised his "heroic" wife after she went through 36 hours of contractions.
"Patsy Palmer told me, 'Get ready to feel a love like you have never felt before'," he said. "And she is absolutely right. It's unbelievable.
"We had a text message from Bertie [Patsy's baby boy] asking Arrabella out on a date. I said, 'No, not until she is 21'," he joked.
McDermott previously admitted that he did not watch the Albert Square drama on New Year's Eve when Ronnie Mitchell swapped her dead son for Kat and Alfie's newborn child.
"When your baby is about to be born you don't choose to watch something like that," he said. "I've watched it since and the aftermath of it. The acting has been very strong and the storyline very good.
"When it is so much more relevant to you then it does become more heartbreaking," he added.
> McDermott: 'Enders tackles tough stories'