The club yesterday completed its summer transfer business by signing Carroll on an initial one-year deal.
Carroll, sold to Liverpool for £35million in January 2011, rejoined as a free agent, having left West Ham United earlier in the summer after his contract at the London Stadium expired.
The Gazette reported on July 20 that United were considering a shock move for the 30-year-old, who is recovering from ankle surgery.
And Carroll has revealed details of the transfer in an interview with NUFC TV.
"We were talking about it, and then I spoke to Lee (Charnley, Newcastle’s managing director) and got involved,” said the Gateshead-born player.
"The last couple of weeks it's been a slow burner, and then I did a medical the other day, and that was it really. It was a bit of a mad one, as we kept it quiet for a while, and then halfway through the journey my phone was non-stop.
"Someone had put something to the press, and my head was all over the place. I couldn't believe it was real. The first hour in (to the journey) it started to sink in. My bags were packed and ready to go. I think it's going to be a better feeling than the first time."
Carroll will “not rush back” from his operation, having been plagued by ankle problems since leaving United.