Bill and Melinda Gates smile at each other during an interview in Kirkland, Washington, Feb. 1, 2019. AP Photo
In this Jan. 9, 1994, file photo, computer mogul Bill Gates III and bride Melinda French greet guests in a reception line at a private estate in Seattle. The couple was married in Hawaii the week prior. AP Photo
Bill Gates Chairman and CEO of Microsoft and his wife Melinda listens to Josh Stack, 15, explaining the Demopolis, Alabama web site on a computer at the Demopolis Public library, February 24, 1998. Reuters.
Bill Gates contends with an ill-fitting hard hat while his wife, Melinda Gates, looks on in Seattle at the groundbreaking of the University of Washington's new law school facility, William H. Gates Hall, May 4, 2001. AP Photo
Bill Gates and his wife Melinda, left, walk on a street in Dhaka, Bangladesh, Dec. 5, 2005. AP Photo
US Microsoft owner Bill Gates addresses a youth forum on HIV/AIDS at the University of Witwatersrand in Johannesburg, 22 September 2003, as his wife Melinda Gates and former South African President Nelson Mandela listen to him. AFP Photo
Britain's Queen Elizabeth II presents Microsoft tycoon Bill Gates with his honorary knighthood at Buckingham Palace, London, Wednesday March 2, 2005 watched by his wife Melinda. AFP
Bill Gates and his wife Melinda hold a press conference in New York 02 December to announce a 100 million USD gift to establish the Bill and Melinda Gates Children's Vaccine Program. AFP
Melinda Gates smiles at her husband Bill Gates during the opening news conference for AIDS 2006, the XVI International AIDS conference in Toronto, August 13, 2006. Reuters
Bill Gates shares the stage with his wife Melinda during the 123rd Stanford commencement ceremony in Stanford, California. AFP
Microsoft Corp co-founder Bill Gates and his wife Melinda Gates watch the swimming events at the National Aquatics Center during the Beijing 2008 Olympic Games, in Beijing, China August 10, 2008. Reuters
Bill and Melinda Gates attend a debate on the 2030 Sustainable Development Goals in Brussels January 22, 2015. Reuters
Philanthropist and co-founder of Microsoft, Bill Gates and his wife Melinda talk, after being awarded Commanders of the Legion of Honor at the Elysee Palace in Paris, France, April 21, 2017. Reuters
Bill and Melinda Gates smile at each other during an interview in Kirkland, Washington, Feb. 1, 2019. AP Photo
In this Jan. 9, 1994, file photo, computer mogul Bill Gates III and bride Melinda French greet guests in a reception line at a private estate in Seattle. The couple was married in Hawaii the week prior. AP Photo
Bill Gates Chairman and CEO of Microsoft and his wife Melinda listens to Josh Stack, 15, explaining the Demopolis, Alabama web site on a computer at the Demopolis Public library, February 24, 1998. Reuters.
Bill Gates contends with an ill-fitting hard hat while his wife, Melinda Gates, looks on in Seattle at the groundbreaking of the University of Washington's new law school facility, William H. Gates Hall, May 4, 2001. AP Photo
Bill Gates and his wife Melinda, left, walk on a street in Dhaka, Bangladesh, Dec. 5, 2005. AP Photo
US Microsoft owner Bill Gates addresses a youth forum on HIV/AIDS at the University of Witwatersrand in Johannesburg, 22 September 2003, as his wife Melinda Gates and former South African President Nelson Mandela listen to him. AFP Photo
Britain's Queen Elizabeth II presents Microsoft tycoon Bill Gates with his honorary knighthood at Buckingham Palace, London, Wednesday March 2, 2005 watched by his wife Melinda. AFP
Bill Gates and his wife Melinda hold a press conference in New York 02 December to announce a 100 million USD gift to establish the Bill and Melinda Gates Children's Vaccine Program. AFP
Melinda Gates smiles at her husband Bill Gates during the opening news conference for AIDS 2006, the XVI International AIDS conference in Toronto, August 13, 2006. Reuters
Bill Gates shares the stage with his wife Melinda during the 123rd Stanford commencement ceremony in Stanford, California. AFP
Microsoft Corp co-founder Bill Gates and his wife Melinda Gates watch the swimming events at the National Aquatics Center during the Beijing 2008 Olympic Games, in Beijing, China August 10, 2008. Reuters
Bill and Melinda Gates attend a debate on the 2030 Sustainable Development Goals in Brussels January 22, 2015. Reuters
Philanthropist and co-founder of Microsoft, Bill Gates and his wife Melinda talk, after being awarded Commanders of the Legion of Honor at the Elysee Palace in Paris, France, April 21, 2017. Reuters
Bill and Melinda Gates smile at each other during an interview in Kirkland, Washington, Feb. 1, 2019. AP Photo