Selwood's tragic passing in Perth on Saturday came just three months after his identical twin and fellow former AFL player Troy Selwood died.
Members of the AFL's famous Selwood family, Adam and Troy were brothers of Geelong champion Joel and former Eagles and Cats midfielder Scott.
Adam Selwood played 187 games for West Coast, including the 2006 premiership, before retiring from football in 2013.
"We are heartbroken by the passing of Adam earlier today. Words cannot express the grief and sadness we feel," the Selwood family said in a statement via the AFL on Saturday.
"Adam was a loving husband, and an incredible father to Lenny and Billie. We are devastated to lose such a wonderful husband, father, son and brother.
"We will miss Adam deeply - his spirit, his kindness, and the joy he brought to every room. His determination, the lessons he shared, and his infectious personality will stay with us always.
"Adam had a unique ability to make people feel special, and our family was lucky to experience that every day.
"We kindly ask for privacy as we navigate this difficult time."
Troy Selwood, who played 75 games for the Brisbane Lions, died in February and was remembered by Adam as a "built-in best mate" at his funeral.
Adam declared writing the eulogy was the "hardest thing" he had ever had to do.
"Having an identical twin is both a rare privilege and wonderfully complex," Adam said at Troy's memorial service at GMHBA Stadium in February.
"A twin is more than a sibling, they are a constant presence, a built-in best mate and someone who understands you in a way that no-one ever could.
"Troy wasn't just my brother; he was my mirror, my fiercest competitor, my greatest ally and the one person that knew what I was always thinking.
"Losing him has left a massive hole in my life."
Adam Selwood's premiership teammate Adam Hunter died in the same week as Troy Selwood in February.
Hunter, who also played alongside Scott Selwood with the Eagles, was 43.
West Coast's 2006 premiership coach and current head of football John Worsfold led tributes to Adam Selwood on Saturday.
"Adam was a great teammate who loved the club and loved his footy," Worsfold said in a statement.
"He always put his mates and team first, and he would be saying that now. He would be wanting to see our Club grow and return to having on-field success once again.
"We drafted him at 18 and watched him grow as a player and person.
"We got to know the Selwood family so well over the years, and they are such wonderful people who our hearts go out to more than anything today."
AFL chief executive Andrew Dillon said he could not imagine the pain of the Selwood family.
"On behalf of the AFL and all of our clubs, I want to send our love to his wife Fiona and their two children, to Maree and Bryce Selwood, Joel and Scott, and their families, and all of Adam's many friends and colleagues and past team mates at West Coast and across football," Dillon said in a statement.
Originally from Bendigo, Adam Selwood moved to Perth when he was drafted by West Coast in 2002.
He joined the Eagles' coaching ranks after his retirement as a player, working with the club's AFL and AFLW teams.
Selwood was also West Coast's inaugural head of female football, charged with setting up the club's AFLW team.
West Coast will pay tribute to Selwood at their home game against St Kilda at Optus Stadium on Sunday.
Scott Selwood was due to be at the MCG on Saturday as an assistant to Collingwood coach Craig McRae, but was granted personal leave.
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