Luis Enrique resigned from the role in June to spend more time with his daughter Xana after she was diagnosed with cancer, later passing away in August aged nine.
His long-time assistant Moreno succeeded him and helped Spain qualify for Euro 2020 as group winners but had an unceremonious end to his short time as coach and left the role after Spain's 5-0 win over Romania on November 18.
Moreno declined to give a news conference after that match as confusion reigned but the following day it was confirmed Luis Enrique was to return as the team's head coach.
"The only person responsible for Robert Moreno not being in my coaching staff is me," Luis Enrique told a news conference at his unveiling as Spain coach on Wednesday.
"He came to see me in my house and told me he wanted to lead the team at Euro 2020 and afterwards he would be happy to be my assistant coach again.
"I understand that he has worked very hard to be the coach and that he is ambitious - but for me that is disloyal. I would never do something like that and I don't want someone with those characteristics in my staff."
Moreno first worked alongside Luis Enrique at Barcelona's B team and followed him to AS Roma, Celta Vigo and back to Barca, later joining his coaching staff when he landed the Spain job in July 2018.
"I understand his decision but cannot agree with it and told him I didn't want him as my assistant and that I felt strong," added Luis Enrique.
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"Ambition is to be encouraged but excessive ambition is a defect, not a virtue."
The former Barcelona coach said he did not inform the Spanish national federation (RFEF) president Luis Rubiales of his intention to return to the role but he and sporting director Jose Francisco Molina offered him the chance to come back.
"This has not been a good year for me but I want to look forward and I want to pay back the faith that has been shown in me," he added.