Brugge revealed on 4 August that the 31-year-old Belgium worldwide had agreed a five-year deal.
Mignolet, capped 21 times by Belgium, joined Liverpool from Sunderland six years ago and made 204 appearances for the club, winning the Champions League in 2019.
Liverpool agreed to sell Mignolet to Club Brugge in a deal that could be worth up to £8m, with the capture of Adrian on a free transfer good business for the Anfield club.
Simon expressed his pleasure at his time spent at Liverpool and said that the current squad was the best he had played with.
Age doesn't really factor into keepers' effectiveness as West Ham's now number one keeper, 34-year-old Fabianski has shown us.
Adrian is hoping to push Alisson for first-team minutes this season, and let us West Ham supporters tell you: if this happens you're in some massive trouble.
Obviously I'm really happy to be here.
The football player was on the bench because on Sunday the Reds lost the Community Shield versus Citizens. That same evening, Club Brugge announced they had signed "one of the best goalkeepers in the Premier League".
"So I've come here to fight for all the competitions".
The Hammers released him on a free transfer at the end of last season.
"So we're going to fight for it, and try hard to get them".
Mignolet, who joined Liverpool in 2013, looked set to remain at Anfield after receiving plenty of praise for maintaining his professionalism as he watched from the sidelines.
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