Francomb spent three-months on loan at the Dons last season and will link up with Neal Ardley's squad ahead of the new campaign.
"We were very sorry to lose George when he went back to Norwich because he was probably the highlight for us in a struggling team at the time," Ardley told the Dons' official site. "I really enjoyed working with him then because you could see the quality that he had. As soon as I knew that the player would be leaving Norwich I threw my hat into the ring. I spoke to his agent in early May because I knew that I would have to do a bit of work to get him. I had to try and put the budget in place so that we could make an offer that could bring George back here."