Adam Treloar is finally a Magpie after Collingwood and Greater Western Sydney concluded their protracted trade negotiations for the young star on Wednesday afternoon.

As expected, Collingwood gave up its first-round picks this year (No.7 overall) and next year's first pick for Treloar, while it also gave No.65 to the Giants.

In addition to Treloar, the Giants also passed their second-round draft pick this year (No.28 overall) back to the Pies.

The Magpies will now look to broker a trade for wantaway Brisbane Lions midfielder James Aish before the NAB AFL Trade Period closes at 2pm on Thursday.

Treloar came out of contract at the end of this season and requested a trade to Collingwood on the Monday after the home and away season finished.

The Magpies and Giants were believed to have finalised an in-principle agreement last week, but the negotiations dragged on and even became fractious at times, especially when it emerged Treloar had undergone post-season surgery without the Giants' knowledge following a medical test at Collingwood.

Treloar, 22, joins the Magpies on a long-term deal believed to be worth about $750,000 a season, having been hotly pursued by Richmond and North Melbourne before settling on Collingwood as his new home.

The Victorian played 79 games in his four seasons at GWS, emerging as one of the competition's most existing young on-ballers.

Treloar finished runner-up in the Giants' best and fairest award this season after averaging 27.5 disposals a game (ranked first at the club).

This followed his top-five finishes in the 2013 (fifth) and 2014 (fourth) award counts, and a top-10 finish in the Giants' inaugural 2012 season (ninth).

Speculation about Treloar's future raged on for much of the 2015 season, and became more and more heightened as the Giants progressively re-signed fellow star youngsters such as Jeremy Cameron, Dylan Shiel, Devon Smith, Stephen Coniglio and Will Hoskin-Elliott.

Treloar was one of the Giants' 17-year-old concession selections ahead of their inaugural AFL season, along with the likes of Cameron, Shiel, Tom Bugg, Nathan Wilson and Jack Hombsch (since traded to Port Adelaide).

The trade wasn't confirmed until Wednesday, but a club-produced video with Treloar in Pies colours was leaked online late Tuesday night.

Collingwood and the AFL have investigated the unauthorised publication of Collingwood content via social media on Tuesday evening. The material was placed on the network in preparation for an announcement involving Adam Treloar's now consummated trade to Collingwood and was inadvertently provisioned earlier than it was intended.