[{item:{id:168652},connected_realm_id:1602,last_modified:1596719280},{item:{id:168652},connected_realm_id:1602,last_modified:1596719280},{item:{id:168652},connected_realm_id:1602,last_modified:1596719280},{item:{id:168652},connected_realm_id:1602,last_modified:1596719280},{item:{id:168652},connected_realm_id:1602,last_modified:2},{item:{id:168652},connected_realm_id:1602,last_modified:3},{item:{id:168652},connected_realm_id:1602,last_modified:4},{item:{id:168652},connected_realm_id:1602,last_modified:5},{item:{id:168652},connected_realm_id:1602,last_modified:1596719280},{item:{id:168652},connected_realm_id:1602,last_modified:1596719280},{item:{id:168652},connected_realm_id:1603,last_modified:1596719267},{item:{id:168652},connected_realm_id:1603,last_modified:1596719267},{item:{id:168652},connected_realm_id:1603,last_modified:1596719267},{item:{id:168652},connected_realm_id:1603,last_modified:1596719267},{item:{id:168652},connected_realm_id:1603,last_modified:1},{item:{id:168652},connected_realm_id:1603,last_modified:2},{item:{id:168652},connected_realm_id:1603,last_modified:3},{item:{id:168652},connected_realm_id:1603,last_modified:4},{item:{id:168652},connected_realm_id:1603,last_modified:5},{item:{id:168652},connected_realm_id:1603,last_modified:1596719267}]

db.collection.aggregate([{$group:{_id:{connected_realm_id:"$connected_realm_id",latest_timestamp:{$max:"$last_modified"},},data:{$push:"$$ROOT"}}},{"$unwind":"$data"},{$group:{_id:{connected_realm_id:"$data.connected_realm_id"},"data":{"$max":"$data.last_modified"},"item":{"$first":"$data.item.id"}}},{$project:{"connected_realm_id":"$_id.connected_realm_id","last_modified":"$data","item":1,"_id":0}},{"$group":{"_id":"$item","groupedBy":{"$push":"$$ROOT"}}}])