It has been reported the move was in the works up to a year ago, and there are suggestions Franklin had made up his mind before entering the Grand Final.
"I hadn't, I truly hadn't made my decision before the Grand Final," Franklin told AFL.com.au.
"I went in there just wanting to win the Grand Final and was able to do it and leave a two-time premiership player, and hopefully there's a few more to come.
"I made my decision pretty much at the last minute so Sydney, to their credit, have done a good job and I'm happy to be there."
Franklin sat down with his teammates on Tuesday to deliver the news.
"The boys have been really good," Franklin said.
"I've had some close mates at the footy club for a long time. I sat down and had a chat to a few of them yesterday (Tuesday) and they've taken it really well.
"From the start, though, the footy club has been a massive part of my life and they've made me the person I am today. Alastair Clarkson too, full credit to him. He's been amazing during this period.
"It's obviously tough on him and his family. I just want to say thanks to the Hawthorn Football Club. They've been great to me."
Now that he's made the decision, he says he can't wait to make the move north.
"I'm excited," Franklin said.
"Yeah, looking forward to getting up to Sydney. It's a great footy club and as I said I had to pack my bags up at Hawthorn and saying goodbye to the boys is something very tough, and upsetting too."
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