The 28-year-old defender joins the Hammers on a four-year contract, with the option of a further year.
Forest are making ANOTHER signing and are also competing with Atalanta for Chelsea wing-back Emerson.
Both players are out of contract in 2024, so Chelsea could opt to let them leave this summer.
If the defender leaves this summer, Lyon will have first dibs on him...
The 27-year-old represented Italy at this summer's European Championship but has failed to make an impact at Chelsea.
Marcos Alonso and Emerson Palmieri will be allowed to leave Chelsea due to the form of Englishman Ben Chilwell.
Emerson has fallen down the pecking order at Chelsea and will be allowed to leave for £17million.
Chelsea are now unbeaten in 11 matches in all competitions under Tuchel.
Chelsea and Brazil defender Emerson could be on his way to Italy in January after being linked with two of Europe's elite.
Chelsea are ready to take a big hit on £160million-worth of players.
Chelsea need to make room for all their new signings...
Lampard's 'controlling style' is driving the defender back to Serie A.
Roberto Mancini has advised one Chelsea defender to return to Serie A if he wants to make Italy's squad for Euro 2021.
"We have people on the edge of the box that ran forward when they should have run backwards."
Remember that Harry Maguire-fuelled new Liverpool contract for Virgil van Dijk. Yeah...forget it.
Alexis Sanchez was never the man Jose Mourinho wanted, just the one that was available.
The Spaniard may finally get a break after the £23m signing of Emerson Palmieri.
Dzeko might be 32 in March, but he's mint. And Emerson might be a reserve, but he's a left-back.
Klopp wanted to sign Palmieri in the summer, but he did his ACL in May. Now he's back...