Transcript for Prince Harry and Meghan Markle's shared passion for humanitarian work: Part 5

Reporter: Tomorrow it's official Harry and Meghan "Husband" and "Wife." But even before the vows their devotion has been on full display not just to each other, but to the causes they support. Clearly both Harry and Meghan have a side of them that is about giving back, about doing good, about helping others. Reporter: In fact it was part of that first date spark that attracted them to each other. It was one of the first things we started talking about when we met was just the different things that we wanted to do in the world and how passionate we were about seeing change. I think that was that's what got date two in the books. Plenty to talk about. Reporter: In the nearly six months since their engagement, they've been side by side celebrating sports for disadvantaged youth, attending an anniversary service for the racially motivated murder of a black teen. Visiting a cafe that feeds the homeless. They are both completely charming. It was actually pleasant. I was surprised how well informed them were. Reporter: Their shared passion is rooted in a powerful legacy. For Harry a father whose life has been devoted to philanthropy and a mother dubbed the people's princess for her humanitarian work across the globe. Harry is his mother's son. He can walk into a room and light it up. He's incredibly warm. Busy hugging kids. We see Meghan already doing that. Reporter: Diana was determined to raise her sons with a social conscience bringing them to visit homeless shelters, as seen in this photo posted by the palace. She famously brought awareness to the plight of people with HIV and AIDS. That's something that William and I hope to carry on in her name, as much as we can, anyway. But, you know, sometime sometimes it takes something like that to, to really bring it home to people about, to what's going on out there. Reporter: Harry has found his own passions like the invictus games for wounded veterans. The site of his first public outing with Meghan. And tackling the stigma of mental health. It is ok to suffer, but as long as you talk about it. It is not a weakness. Weakness is having a problem and not recognizing it and not solving that problem. Reporter: And he has mirrored his mother's commitments campaigning against landmines. And naming his HIV charity sentebale or "Forget me not" in his mother's honor. I suppose it's my little way my little connection of holding onto my mother. Reporter: Meghan is also following in the example of her mother, according to Andrew Morton. In his new book he describes how Meghan's mother, a social worker, expoy age to those less fortunate Her mother Doria took her to Mexico, to Jamaica, some of the shanty towns there to give her a sense of-- that life wasn't quite as cozy and as comfortable as that in los Feliz. Reporter: And by age 11, Meghan was a budding activist even confronting gender inequality in advertising. Women are fighting greasy pots and pans with ivory clear. She was profiled on Nick news. It's always mom does this and mom does that. I was furious. She began a letter writing campaign. So I was wondering if you would be able to change your commercial to people all over America. Three months later, proctor and gamble changed the commercial. People are fighting greasy pots and pans with ivory clear. You can really make a difference for not just yourself but lots of other people. And once she become a well-known actress on "Suits" there were more opportunities to give back. Even with Meghan's crazy schedule as an actor, she's always made time for philanthropic endeavors. Like taking her fight against gender inequality to a bigger stage the U.N. I am proud to be a woman and a feminist. It isn't enough to simply talk about equality. One must believe in it. Reporter: Meghan later travelled to India with world vison's Lara Dewar. She's the kind of person who always reaches out to shake a hand first. Looks people in the eye, knows their name and uses it in conversation. She's a very engaging person. Everywhere we went, Meghan always has a notebook with her. She is interested in following up, and writing stories, and using her platform to really amplify the voices of the world's most vulnerable children. Reporter: By the time Meghan met Harry each had a well-honed sense of purpose and duty. I am also incredibly grateful that the woman I am about to marry, Meghan, will be joining me in this work, of which she too is hugely excited to take part in. Reporter: In that spirit among the invitees to Tomo wedding celebration hundreds of people selected for their service to their communities. They're a global power couple. And they're really gonna be able to make a difference to people's lives.

This transcript has been automatically generated and may not be 100% accurate.