Toby Greene will be joining Geelong.
Greene has been linked with the Cats for the past three weeks, with the Giants captain flagging his intention to return to Victoria to be closer to family.
He will be reunited with great mate Jeremy Cameron.
"I must admit, I expected this," Outgoing GWS chief executive Dave Matthews said on SEN.
"I think the fact the decision dragged out really reflects how torn he's been and how much he feels a part of the Giants. I mean, he'll always be a Giant.
"It was just a really difficult one for him, and I think that's probably a good reflection on our club that it's not an easy decision for him, and that tells you that you know the club's in good shape, and he feels such a strong affection for the playing group and enjoys playing for Adam Kingsley and all the things that go with it.
"He's been a very celebrated figure at our club, a very important person, and I know this has been a really tough decision, and one he's largely made for family reasons."
Matthews spoke on Greene's loyalty to the club, even suggesting his Tribunal visits and record fines were "retribution" or "looking after teammates".
The decision comes shortly after the Cats missed out on star free agent Zak Butters, who nominated the Western Bulldogs as his preferred destination.
Greene joins Jesse Hogan (Collingwood), Jake Stringer and Kieren Briggs (Richmond) as departures from the Giants.
Lachie Whitfield and Harry Himmelberg also loom as potential trade options, with the former linked to St Kilda.
Greene was an inaugural Giant, drafted with Pick 4 in 2011. He has played 282 games, kicking 449 goals. He's earned three All-Australian blazers, two best and fairests and has captained the team since 2022.
