Chelsea have already spent a staggering €466m on defenders since the start of the 2022/23 season and Lacroix's deal takes them past €500m mark as they struggle to find the right fit at the back.
The France international has signed a six-year contract until 2032, with the transfer fee widely reported to be around £51M in what is one of the biggest moves of the summer.
Having missed out on Rennes’ Jérémy Jacquet in January, Alonso was keen to strengthen at the back and spoke in this week’s press conference about the 26 year old who will add immense experience to his side.
“I know Maxence from my time in the Bundesliga,” explained Alonso. “I think his progression and adaptation in the Premier League has been fantastic – not just on the pitch but in terms of personality and leadership, he also has these attributes.
“He is a very reliable player who will give us power in the defensive line. He has an assurance that will have a big, direct impact on the team, I'm sure. So it’s a great signing for now and for the future.
“He has a strong personality, he is mature, and he wants to win. He has a winner’s mentality and also loves to defend. That is something I like as well.”
Lacroix becomes the first player Chelsea have signed for a fee aged 26 or over since the summer of 2022. The Blues are also expected to sign both Jordan Henderson and Danny Welbeck as Alonso adds much needed experience to his side.