This Morning hosts Holly Willoughby and Phillip Schofield spoke to clinical psychologist Dr Anna Colton on Monday about the revelations made by Meghan Markle in her Oprah Winfrey interview.
The Duchess said she suffered from suicidal thoughts during her time in the royal family, saying she "thought it would have solved everything for everyone".
She claimed that she went to "the institution" to say she needed help but was told she wasn't allowed to.
She said she was "ashamed" to admit it at the time but "knew that if she didn't say it she would do it", and said it was a "real and frightening and constant thought" but that Prince Harry "cradled her".
Phillip asked: "Bearing in mind that we heard many of those stories surrounding Diana, and the state of her mental health, and whether or not we would hope that any family or institution would learn from things that had happened to them.
"What help should [Meghan] have been offered?"
Dr Colton replied: "The minute she asked for help, she should have been referred to or been given access immediately to a clinical psychologist or a psychiatrist for a proper evaluation of how much need there was.
"Did she need medication, did she need therapy, did she need both?
"There shouldn't have been a delay, those resource are available particularly to that institution, and that's what should have happened immediately.
"To deny people that is to deny people the access to basic healthcare."
Phillip said: "There was one particularly powerful moment within the documentary where Meghan discusses having to get ready to go out to an even at the Royal Albert Hall, to be sobbing when the lights were down, but put the brave face on when the lights came up and people would be looking at her.
"For something like that, when you hear the depth and severity of it, not apparently to be offered help, seems particularly cruel."
Dr Colton agreed: "Well, anybody should be offered help, for a situation like that. If you're experiencing low mood, depression, suicidal ideation, it's not up for debate that you need help, that's a given.
"So, not to offer it is extraordinary, if that is what happened, that's absolutely extraordinary, it's wrong, and as you say, it's cruel.
"Your mental health is the absolute foundation of life, you absolutely have to protect your mental health, it's not an adjunct, it's a necessity.
"Life can't be lived, work can't be done, you can't bring up your kids, you can't have relationships, if your mental health is collapsing, nothing else functions.
"It's the absolute bedrock, it's the foundation, it needs to be of primary importance - it's non disputable."
Watch the full interview on ITV at 9pm on Monday night and on ITV Hub, Courtesy of Harpo Productions/CBS.
If you are struggling and need to talk, the Samaritans operates a free helpline open 24/7 on 116 123. Alternatively, you can email jo@samaritans.org if you'd prefer to write down your feelings or don't wish to be overheard
* This Morning airs weekdays on ITV at 10am
