The pair is set to marry in a traditional Muslim ceremony for which a date has not yet been set, AKDN reported Friday.
Rahim Aga Khan's father, His Highness the Aga Khan -- who is the Spiritual Leader or Imam of the global community of the Shia Ismaili Muslims-- broke the news about the engagement in a press release where he claimed to be "delighted" about the news.
Spears, who got numerous congratulatory messages via Twitter, thanked her followers for their good wishes through the social site.
"Thank you all for the kind tweets!" she wrote on Friday. "We're very excited! :)"
Thank you all for the kind tweets! We're very excited! :)— Kendra Spears (@Kendra_Spears) April 26, 2013