diff --git a/lib/document.js b/lib/document.js
index 731be3301c7..b9f39a82c12 100644
--- a/lib/document.js
+++ b/lib/document.js
@@ -694,7 +694,6 @@ Document.prototype.$__init = function(doc, opts) {
   init(this, doc, this._doc, opts);
 
   markArraySubdocsPopulated(this, opts.populated);
-
   this.$emit('init', this);
   this.constructor.emit('init', this);
 
@@ -703,7 +702,6 @@ Document.prototype.$__init = function(doc, opts) {
     null;
 
   applyDefaults(this, this.$__.selected, this.$__.exclude, hasIncludedChildren, false, this.$__.skipDefaults);
-
   return this;
 };
 
@@ -746,7 +744,6 @@ function init(self, obj, doc, opts, prefix) {
     }
     path = prefix + i;
     schemaType = docSchema.path(path);
-
     // Should still work if not a model-level discriminator, but should not be
     // necessary. This is *only* to catch the case where we queried using the
     // base model and the discriminated model has a projection
@@ -770,15 +767,14 @@ function init(self, obj, doc, opts, prefix) {
       }
     } else {
       // Retain order when overwriting defaults
-      if (doc.hasOwnProperty(i) && obj[i] !== void 0) {
+      if (doc.hasOwnProperty(i) && obj[i] !== void 0 && !opts.hydratedPopulatedDocs) {
         delete doc[i];
       }
       if (obj[i] === null) {
         doc[i] = schemaType._castNullish(null);
       } else if (obj[i] !== undefined) {
         const wasPopulated = obj[i].$__ == null ? null : obj[i].$__.wasPopulated;
-
-        if (schemaType && !wasPopulated) {
+        if ((schemaType && !wasPopulated) && !opts.hydratedPopulatedDocs) {
           try {
             if (opts && opts.setters) {
               // Call applySetters with `init = false` because otherwise setters are a noop
diff --git a/lib/model.js b/lib/model.js
index 93e34c2eb33..a596c864833 100644
--- a/lib/model.js
+++ b/lib/model.js
@@ -3830,6 +3830,7 @@ Model.buildBulkWriteOperations = function buildBulkWriteOperations(documents, op
  * @param {Object|String|String[]} [projection] optional projection containing which fields should be selected for this document
  * @param {Object} [options] optional options
  * @param {Boolean} [options.setters=false] if true, apply schema setters when hydrating
+ * @param {Boolean} [options.hydratedPopulatedDocs=false] if true, populates the docs if passing pre-populated data
  * @return {Document} document instance
  * @api public
  */
@@ -3843,7 +3844,6 @@ Model.hydrate = function(obj, projection, options) {
     }
     obj = applyProjection(obj, projection);
   }
-
   const document = require('./queryHelpers').createModel(this, obj, projection);
   document.$init(obj, options);
   return document;
diff --git a/test/model.hydrate.test.js b/test/model.hydrate.test.js
index 6cdc333ce8d..bc6632f5b15 100644
--- a/test/model.hydrate.test.js
+++ b/test/model.hydrate.test.js
@@ -99,5 +99,23 @@ describe('model', function() {
       assert.equal(hydrated.test, 'test');
       assert.deepEqual(hydrated.schema.tree, C.schema.tree);
     });
+    it('should deeply hydrate the document with the `hydratedPopulatedDocs` option (gh-4727)', async function() {
+      const userSchema = new Schema({
+        name: String
+      });
+      const companySchema = new Schema({
+        name: String,
+        users: [{ ref: 'User', type: Schema.Types.ObjectId }]
+      });
+
+      db.model('UserTestHydrate', userSchema);
+      const Company = db.model('CompanyTestHyrdrate', companySchema);
+
+      const users = [{ _id: new mongoose.Types.ObjectId(), name: 'Val' }];
+      const company = { _id: new mongoose.Types.ObjectId(), name: 'Booster', users: [users[0]] };
+
+      const C = Company.hydrate(company, null, { hydratedPopulatedDocs: true });
+      assert.equal(C.users[0].name, 'Val');
+    });
   });
 });
diff --git a/test/types/models.test.ts b/test/types/models.test.ts
index 9bf423f136f..61298be836d 100644
--- a/test/types/models.test.ts
+++ b/test/types/models.test.ts
@@ -880,3 +880,23 @@ async function gh13999() {
     }
   }
 }
+
+function gh4727() {
+  const userSchema = new mongoose.Schema({
+    name: String
+  });
+  const companySchema = new mongoose.Schema({
+    name: String,
+    users: [{ ref: 'User', type: mongoose.Schema.Types.ObjectId }]
+  });
+
+  mongoose.model('UserTestHydrate', userSchema);
+  const Company = mongoose.model('CompanyTestHyrdrate', companySchema);
+
+  const users = [{ _id: new mongoose.Types.ObjectId(), name: 'Val' }];
+  const company = { _id: new mongoose.Types.ObjectId(), name: 'Booster', users: [users[0]] };
+
+  return Company.hydrate(company, {}, { hydratedPopulatedDocs: true });
+
+
+}
diff --git a/types/models.d.ts b/types/models.d.ts
index 67731cc3eb0..a77aa25525e 100644
--- a/types/models.d.ts
+++ b/types/models.d.ts
@@ -37,6 +37,11 @@ declare module 'mongoose' {
     skipValidation?: boolean;
   }
 
+  interface HydrateOptions {
+    setters?: boolean;
+    hydratedPopulatedDocs?: boolean;
+  }
+
   interface InsertManyOptions extends
     PopulateOption,
     SessionOption {
@@ -371,7 +376,7 @@ declare module 'mongoose' {
      * Shortcut for creating a new Document from existing raw data, pre-saved in the DB.
      * The document returned has no paths marked as modified initially.
      */
-    hydrate(obj: any, projection?: AnyObject, options?: { setters?: boolean }): THydratedDocumentType;
+    hydrate(obj: any, projection?: AnyObject, options?: HydrateOptions): THydratedDocumentType;
 
     /**
      * This function is responsible for building [indexes](https://www.mongodb.com/docs/manual/indexes/),