Cam McCarthy says he shed a tear when the news came through that he would finally return to AFL football after he was traded from Greater Western Sydney to Fremantle.

The 21-year-old lifelong Fremantle supporter tried to get to the Freo Dockers during last year's NAB AFL Trade Period but failed as GWS held him to the final two years of his contract.

McCarthy sat out 2016 and remained at home in Perth to deal with some mental health issues.

The Giants traded him to Freo on Tuesday as part of a deal that involved Freo giving up pick No.3 in the NAB AFL Draft in return for McCarthy plus a first-round pick (currently No.7), a second-round pick (currently No.35) and a fourth-round pick (currently No.73).

Fremantle's list manager Brad Lloyd called McCarthy with the good news on Tuesday and the youngster said it was an emotional moment.

"It's overwhelming to tell you the truth," McCarthy said.  

"I was sitting at home yesterday and I got a call from Lloydy, Brad Lloyd, and the feeling was pretty numbing. I was just sitting back in my chair and I had a bit of a tear and it's just been a long, long year and I am so excited now."

McCarthy went to Fremantle Oval on Wednesday morning to meet some of Freo's staff. He spoke to coach Ross Lyon briefly and did a running session with Brownlow medallist Nat Fyfe.

Free agent Mayne heading to Collingwood

He has spent the year training three times a week with his WAFL club South Fremantle. He has also been working with a personal trainer to keep himself in shape throughout 2016.

South Fremantle coach Todd Curley told AFL.com.au last month that McCarthy was in good shape and should not have any issues getting back into the AFL system.

McCarthy said he felt strong but he was aware he has a lot of work to do.

"I've done a lot of gym work lately and I've sort of got stronger in my upper body and my legs, so I feel like I've got a lot more power when I'm running," McCarthy said.

"But obviously there is going to be a lot more work being back on a list and back training full-time. Hopefully I can build that and the aerobic capacity and really have a good pre-season."

McCarthy kicked 35 goals in 20 games for the Giants in 2015. He will be seen as a replacement of sorts for retired Fremantle great Matthew Pavlich but he said he did not feel any added pressure.

"I'm not really thinking about that too much," McCarthy said.

"I just want to start pre-season and earn the respect of my teammates and really give it a good hot crack.

"I'm starting from the bottom a bit, I guess."

McCarthy said he would seek out Pavlich for advice if Freo games record-holder visited the club at any stage.

McCarthy's trade was the first of a big period for Freo.

Chris Mayne is officially headed to Collingwood as an unrestricted free agent.

Freo received a second-round pick (currently No.23) as compensation for Mayne's exit. They now have two second-round picks after entering the trade period without one.

That will pave the way for deals to be negotiated to secure Hawthorn speedster Bradley Hill and Geelong forward Shane Kersten in the coming days.