Soon after the keynote was delivered at the Apple WWDC in San Francisco on Monday, Koum tweeted: "very flattering to see Apple "borrow" numerous WhatsApp features into iMessage in iOS 8 #innovation."
While he did not specify the features, his tweet points to Apple's new version of iMessage that now has the option of inserting audio, video and location information into conversations.
These features are already available on WhatsApp.
Interestingly, last year when Apple had launched its colourful and cheaper iPhone 5C for emerging markets like China, rival Nokia bought out a campaign stating: "Imitation is the best form of flattery."
Earlier this year in February, WhatsApp had surprised the market by announcing that social networking giant Facebook is acquiring it for USD 19 billion, one of the biggest deals in the technology sector.
On the iMessage feature, Apple said: "Messages in iOS 8 makes it easy to capture any sound your voice, a song, or a big laugh and make it part of the conversation. Simply touch and hold the new microphone button to record your message. Then swipe to send it."
The new Messages app lets you share what you are seeing almost as you are seeing it, Apple added.
Besides, the app lets the user start a group conversation and give it a name.
"Easily include who you want, drop who you don't, and leave the conversation whenever you want. Or turn on 'Do Not Disturb' and then read through the messages when you have time," it added.