The burly ruckman played 18 games for the Cats in 2009 but watched the grand final from the sidelines after Geelong coach Mark Thompson opted to play Brad Ottens and Mark Blake against St Kilda.
Mumford returns to Skilled Stadium this weekend when the Swans play Geelong and he said there was no lingering anger at missing out on the flag.
"I've moved on, as they've moved on. We're both pretty happy now," he said.
"Of course, you're going to be upset about missing out on a grand final but I'll look forward to playing in one this year with the Swans, hopefully."
Mumford will line up against Geelong as the Swans' lead ruckman after regular partner Mark Seaby broke his ankle against the Brisbane Lions in round six.
"I was happy sharing the load with Seabs. I guess it's a great opportunity for me to be playing more game time and really cement my spot now. I feel like I've stepped up enough this year that I can take that on," he said.
However, he will be denied the chance to battle the man whose presence denied him a premiership medallion after Ottens was ruled out for up to eight weeks with a foot injury.
"You want to play against the best players you can each week but Blake's still a very good ruckman so we'll see how we go," Mumford said.
"You always want to play well against your old side but I don't really feel any extra pressure to do so."
Meanwhile, Swans coach Paul Roos said he was leaning towards using rookie Mike Pyke as Mumford's backup during Seaby's absence.
"We just think he's improved significantly ... and we're not talking about a short-term injury," he said.
"You could argue that you could use Jesse [White], and he did really well on the weekend, but does that stunt his development? Our structures have been really good with Jesse up forward.
"We've got to think about Seaby's replacement but also the rest of the team as well."
While Roos did not confirm Pyke's inclusion, the sight of the former Canadian rugby union international running clearance drills with the likes of Brett Kirk, Jude Bolton and Jarrad McVeigh at Tuesday's training session added further weight to the coach's suggestion.
