diff --git a/mod.ts b/mod.ts
index 2d482b4..74e1947 100644
--- a/mod.ts
+++ b/mod.ts
@@ -31,6 +31,11 @@ export interface SessionFlavor<S> {
      */
     get session(): S;
     set session(session: S | undefined);
+    /**
+     * Used by the session plugin to store the current session key, if it
+     * exists.
+     */
+    sessionKey: string | undefined;
 }
 /**
  * A lazy session flavor is a context flavor that holds a promise of some
@@ -166,6 +171,15 @@ type MultiSessionOptionsRecord<
     [K in keyof S]: SessionOptions<S[K], C>;
 };
 
+function setSessionKey(ctx: Context, key?: string) {
+    Object.defineProperty(ctx, "sessionKey", {
+        value: key,
+        writable: false,
+        configurable: false,
+        enumerable: true,
+    });
+}
+
 /**
  * Session middleware provides a persistent data storage for your bot. You can
  * use it to let your bot remember any data you want, for example the messages
@@ -233,6 +247,7 @@ function strictSingleSession<S, C extends Context>(
             initial,
         );
         const key = await getSessionKey(ctx);
+        setSessionKey(ctx, key);
         await propSession.init(key, { custom, lazy: false });
         await next(); // no catch: do not write back if middleware throws
         await propSession.finish();
@@ -257,6 +272,7 @@ function strictMultiSession<S, C extends Context>(
                 initial,
             );
             const key = await getSessionKey(ctx);
+            setSessionKey(ctx, key);
             await s.init(key, { custom, lazy: false });
             return s;
         }));
@@ -314,6 +330,7 @@ export function lazySession<S, C extends Context>(
             initial,
         );
         const key = await getSessionKey(ctx);
+        setSessionKey(ctx, key);
         await propSession.init(key, { custom, lazy: true });
         await next(); // no catch: do not write back if middleware throws
         await propSession.finish();
diff --git a/test/mod.test.ts b/test/mod.test.ts
index 2323a12..58d44aa 100644
--- a/test/mod.test.ts
+++ b/test/mod.test.ts
@@ -253,6 +253,23 @@ describe("session", () => {
         assertEquals(storage.write.calls.length, 4);
         assertEquals(storage.delete.calls.length, 1);
     });
+
+    it("should set ctx.sessionKey", async () => {
+        const storage = {
+            read: () => Promise.resolve(),
+            write: () => {},
+            delete: () => {},
+        };
+
+        const initial = () => ({});
+        type C = Context & SessionFlavor<never>;
+        const composer = new Composer<C>();
+        const ctx = { chatId: 42 } as C;
+        composer.use(session({ storage, initial }));
+
+        await composer.middleware()(ctx, next);
+        assertEquals(ctx.sessionKey, "42");
+    });
 });
 
 describe("multi session", () => {
@@ -471,6 +488,34 @@ describe("multi session", () => {
         assertEquals(storage1.write.calls.length, 4);
         assertEquals(storage1.delete.calls.length, 1);
     });
+
+    it("should set ctx.sessionKey", async () => {
+        const val = {};
+        const storage = {
+            read: () => Promise.resolve(val),
+            write: () => {},
+            delete: () => {},
+        };
+
+        const initial = () => ({});
+        type SessionData = {
+            prop0: Record<string, number>;
+            prop1: Record<string, number>;
+        };
+        type C = Context & SessionFlavor<SessionData>;
+        const composer = new Composer<C>();
+        const ctx = { chatId: 42 } as C;
+        composer.use(
+            session({
+                type: "multi",
+                prop0: { storage, initial },
+                prop1: { storage, initial },
+            }),
+        );
+
+        await composer.middleware()(ctx, next);
+        assertEquals(ctx.sessionKey, "42");
+    });
 });
 
 describe("lazy session", () => {
@@ -757,6 +802,17 @@ describe("lazy session", () => {
         assert(done);
         await p;
     });
+
+    it("should set ctx.sessionKey", async () => {
+        type C = Context & SessionFlavor<never>;
+        const composer = new Composer<C>();
+        const ctx = { chatId: 42 } as C;
+        composer.use(lazySession());
+
+        await composer.middleware()(ctx, next);
+
+        assertEquals(ctx.sessionKey, "42");
+    });
 });
 
 describe("enhanceStorage", () => {