Henderson spent eight years as skipper following Steven Gerrard's departure in 2015 but vacated the armband when he moved to Saudi Pro League side Al Ettifaq - who are coached by Gerrard - in July, but now Liverpool news says Virgil Van Dijk will take over the reigns.
Milner's move to Brighton following the expiry of his Liverpool contract also meant the role of vice-captain at Anfield was vacant, with academy graduate Alexander-Arnold being chosen as his replacement.
Virgil Van Dijk told Liverpool's website: "A really proud day for me, for my wife, for my kids, my family. It's been a special feeling.
"Obviously I'm captain of Holland, that was already such a huge honour, a proud moment as well. But also to be the captain of Liverpool is something that I can't describe at this point.
"It's just something that makes me very proud and I will do everything in my power to make everyone proud and happy with me and the football club.", said Van Dijk to Liverpool news.
Virgil Van Dijk joined Liverpool in 2018 and has made over 200 appearances, winning the Premier League, Champions League, FA Cup, Carabao Cup, UEFA Super Cup, Club World Cup and Community Shield.
In other Liverpool news, Liverpool midfielder Fabinho has completed his £40m move to Saudi Pro League side Al Ittihad.
The Brazil international has signed a three-year deal with the Saudi champions, who are one of four Saudi top-flight clubs to be owned by the country's Public Investment Fund.
In other Liverpool news, Fabinho becomes the second senior midfielder to leave Liverpool for Saudi Arabia this summer after Henderson's move to Al Ettifaq.
Fabinho made more than 200 appearances for Liverpool after signing from Monaco in 2019, winning the Premier League, Champions League, FA Cup, Carabao Cup and UEFA Super Cup.
Liverpool news says, Jurgen Klopp has overhauled his midfield this summer, with Alexis Mac Allister and Dominik Szoboszlai helping to fill the gaps left by Henderson and Fabinho.