A decorated military surgeon operated on a 12-year-old boy's genitals without the consent of his parents.
Cdr Anthony Lambert OBE admitted carrying out the procedure during an unrelated operation at Derriford Hospital in Plymouth, Devon.
Cdr Lambert, who will no longer perform non-emergency operations on children, has apologised along with Plymouth Hospitals NHS Trust.
But the boy's "angry" mother has branded the surgeon "not trustworthy".
The operation was discussed with the General Medical Council (GMC), but the trust was advised to handle it locally.
While the boy from east Cornwall was unconscious and undergoing a hernia operation last year, Cdr Lambert carried out a genital examination.
Cdr Lambert, who was awarded an OBE in 2013 for his work in Afghanistan, felt it was in the "best interests" of the boy to "free adhesions" found on his genitals.
But he did not get consent from the boy's parents who were waiting outside the operating theatre, despite being told he should by a colleague.
Although Cdr Lambert went in to the waiting room, he admitted he left without speaking to the family or calling their name.
The family's lawyer, Andrew Hannam, of Enable Law, said for Cdr Lambert to continue under these circumstances was "shocking for the child and his family"
In a letter of apology, Cdr Lambert said he "should have made more of an effort" to find the parents.
"Why I did not call your name when I left theatre to find you, I do not know," he told the family.
"I unreservedly apologise for the short-fallings in the care I provided to your son."
He also apologised for his "entirely inappropriate" language.
Dr Phil Hughes, medical director for Plymouth Hospitals NHS Trust, sent a letter to the family which said the operation "should not have happened without consent".
He said there should have been "a challenge" to stop the procedure continuing and that an "organisational development intervention" will be put in place with all theatre team members to ensure it does not happen again.