As the IBF's mandatory contender, Joshua had to face the Bulgarian after Wladimir Klitschko made a decision to retire rather than face him in a rematch.
Joshua, who also holds the WBA and IBO titles, has been told he must face IBF mandatory challenger Pulev before December 2 or risk being stripped of that belt.
"I'll be locked away focusing on fight number 20 for the next eight weeks. I'm excited to experience the atmosphere in a sold-out Principality Stadium and aim to give the fans a spectacular night".
The 36-year-old Pulev, who lost his previous world heavyweight title fight against Klitschko inside five rounds, said: "We will not hug and hold, we will not run".
In an ideal world, Joshua will fight Pulev in October, Ortiz in March and then Wilder in the summer of 2018, however, nothing is ever simple in the world of boxing politics and you can imagine a few hurdles to be put in the way of Anthony Joshua. We will stand and fight. "But his style fits perfectly on mine" Pulev states in his Facebook post. My preparations are very intense for the short time I have.
The 27-year-old defeated Klitschko in the 11th round at Wembley Stadium
Pulev has stopped, bludgeoned or knocked out 13 of the 25 men he has beaten and his route from Eastern European obscurity to the world stage was far more hard than the one Joshua was given.
He is also from Bulgaria and that, in heavyweight boxing terms, is simply not sexy enough, which is one of the main reasons the fight will be in Cardiff on October 28 and not in Las Vegas on November 11.
"Anthony Joshua is a great and risky rival", he added. However, by his own admission, he is still learning and Pulev is not the sort of opponent you want to learn against.
But the Cardiff bout, which may well take place under the closed roof at the Principality Stadium, is one Joshua is relishing. It has a retractable roof, making it ideal for the likely chilly fall conditions. Joshua is available at 10/1 to finish the fight in the opening round.
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