Separately, Prince Harry confirmed the couple were an item last November in a Kensington Palace statement criticizing the "wave of abuse and harassment" his then-girlfriend had faced from media outlets.
"We are incredibly happy for Meghan and Harry". "This ring is truly priceless with unmatched cultural significance", she said in an email.
A series of introductions to senior members of the royal family began as early as last autumn, when she met Prince Charles for the first time.
That statement said the couple were "a few months into a relationship" and it was "not right" that Ms Markle should receive such treatment.
Ms Markle credited her American background - and lack of exposure to British tabloids - with allowing her to get to know Prince Harry naturally and organically. Before that, it was occupied by Prince William and Kate Middleton.
It is set to be a busy spring for the royal family, with the wedding and the arrival of a new child for William and Kate providing light relief from the dour political headlines as Britain negotiates Brexit.
Markle revealed the moment was "so sweet and natural and very romantic" and Prince Harry couldn't finish his sentence before she said yes. "Our daughter has always been a kind and loving person".
The Queen and Duke of Edinburgh said they were "delighted for the couple and wish them every happiness", a Buckingham Palace spokesman said.
During the wide-ranging interview, the Prince of Wales told of how the couple were introduced by a mutual friend while on a blind date.
In his office's warning to the media, Prince Harry referred to the sexism and racism directed at ms Markle, whose father is white and her mother African-American. "We were just hit so hard at the beginning with a lot of mistruths". Markle is best known for her role on TV show "Suits" as well as her philanthropic work.
"What I would also like to say is that I really do admire the way that Harry and his brother have drawn attention to mental health conditions all across the country".
Ms Markle may not have been a familiar name in the United Kingdom until recently, but in the U.S. she was known for her role as Rachel Zane in TV legal drama Suits.
Markle spoke to Vanity Fair in September about being "in love" with the Prince.
Speaking to reporters, Prince Harry said he's "thrilled" to be marrying Meghan and added that he knew she was the one from the "very first time" they met, the Guardian reported.
It is one of the smallest homes in Kensington Palace.