Mats Hummels is to rejoin Bayern Munich from Borussia Dortmund for a fee understood to be €38m (£33.8m) including add-ons, subject to a medical.
The 30-year-old central defender signed for Bayern in 2016, after eight years with Dortmund. He won the Bundesliga in each of his three seasons there but lost his place at times during the most recent campaign under Niko Kovac.
Hummels, who has 70 Germany caps, also made the switch from Bayern to Dortmund earlier in his career after coming through the Bayern youth system.
Dortmund have gone on a spending spree this summer, having finished second behind Bayern in the Bundesliga last season. They have completed deals for Nico Schulz (Hoffenheim), Julian Brandt (Bayer Leverkusen) and Thorgen Hazard (Borussia Mönchengladbach) for a total of £66.6m.
They agreed a fee with Chelsea to sell Christian Pulisic for £58.1m and have let Alexander Isak join Real Socidad for £7.1m this summer.
The coach, Lucien Favre, extended his contract with the club this week, signing an extension that will keep him at the club until 2021.