The new feature is hidden in the app, and needs to be turned on by including certain characters.
Heres how it works:
1.
For bold, add asterisks to either side of your text, e.g.
bold2.
For italics, add underscores to either side of the specific word or words, e.g.
For strikethrough, add a tilde (~) to either side of the word or words, e.g.
One can expect this update to roll out to the wider user base in the near future.
With over one billion regular users, WhatsApp is the worlds largest messaging service.
source: www.techworm.net