Rogers has been a Chelsea target for more than two years, although the move coming now is something of a surprise given the club’s 10th-placed Premier League finish last season.
The deal underlines the club’s ability to bounce back from missing out on European football to sign a top target for London rivals Arsenal.
It also suggests Stamford Bridge remains an attractive destination for some of the Premier League’s leading talents.
The pressing question, though, is how Rogers will fit into the side, and what impact his arrival will have on star attacker Cole Palmer.
Rogers was one of the three England players to take a place in Thomas Tuchel’s World Cup squad at Palmer’s expense.
That highlighted the similarities between the pair, but they could also play together, depending on the system employed by new manager Alonso.
The Spaniard has previously used both a back four and back five at his former clubs Real Madrid and Bayer Leverkusen respectively, and there remains uncertainty over his preferred approach just weeks into his tenure.
Rogers and Palmer are both capable of operating in a variety of attacking positions and will compete for minutes with Estevao Willian, Pedro Neto, Jamie Gittens and fellow summer signing Geovany Quenda.
Alejandro Garnacho is being sold to make way, but it remains a hefty group of options for a club playing only one game per week next season.
Off the pitch, Rogers and Palmer have described each other as best friends in football after progressing through Manchester City’s academy together.
Palmer’s famous “Cold Palmer” celebration was inspired by Rogers, who first did the pose as a Middlesbrough player.
The move may prompt further debate over ownership of the celebration, which has been trademarked in the UK’s Intellectual Property Office.
There will also be debate about who plays the number 10 role, yet it is a problem Alonso is likely to welcome.