No he was not; though his mother, the also very stupid/dumb and mentally crippled Spencer ( The Spencer family has been known, for the past several 100s of years, as being nasty, some down right EVIL, and/or NUTS...it's genetic! ) said, when both boys were quite young, that William took after his father and was very intelligent and that Harry took after her and was STUPID.
Throughout most of Harry's life, he was coddled ( extremely spoiled by his mother! ), and protected by EVERYONE in the family as well as his tutors.
That is terrible, I mean what Princess Diana said about her second son‘s intelligence.
How could a mother say such a horrible thing about her child, even if it were true? 🙁