She had trained at the Sandhurst military academy with Prince William and was one of the many officer cadets graduating at the same time as the royal in last December's passing out ceremony, attended by the Queen.
"Prince William was deeply saddened to hear the tragic news of Jo Dyer's death," a Clarence House spokesperson said.
"Jo was a close friend of his at Sandhurst and he is very much thinking of her family and friends right now and they will remain in his thoughts and prayers."
2nd Lt Dyer completed officer training at Sandhurst after graduating from Oxford University. Described as a "talented and energetic officer" by her commanding officer, Lieutenant Colonel Mark Kenyon, she had only been in Iraq for a few weeks when she died.
Corporal Kris O'Neill, 26, Private Eleanor Dlugosz, 19, and Kingsman Adam James Smith, also died in the Basra blast, which saw only the third and fourth female fatalities among UK forces since the 2003 Iraq invasion.
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