The first example for an endohedral transition-metal atom (Ru) sequestered in a seven-coordinate surrounding of rare-earth metal atoms (Pr) has been found for {RuPr3}Cl-3. The monocapped trigonal prisms of Pr atoms share two rectangular faces, forming a zigzag chain with Ru-Ru distances of 308 pm. Intracluster bonding is dominated by Ru-Pr bonding with very little Ru-Ru bonding.