Question: Lynda Bird Johnson Robb is the oldest living child of a U.S. President following the death of a United States Army officer who served as the United States Ambassador to where?
Context: Michael Edward Reagan (born John Flaugher; March 18, 1945) is an American political commentator, Republican strategist, former radio talk show host, and author.  He is the adopted son of former U.S. President Ronald Reagan and his first wife, Jane Wyman.  He is the oldest living child of the late U.S. President. John Sheldon Doud Eisenhower (August 3, 1922 – December 21, 2013) was a United States Army officer and military historian.  As a son of President Dwight D. Eisenhower, he ended his military career as a decorated brigadier-general.  In the administration of President Richard Nixon (his father’s vice-president), he served as United States Ambassador to Belgium. Lynda Bird Johnson Robb (born March 19, 1944) is an American chairwoman and magazine editor who served as First Lady of Virginia from 1982 to 1986, before that as Second Lady of Virginia from 1978 to 1982.  She is the elder of the two daughters of former United States President Lyndon Baines Johnson and former First Lady Lady Bird Johnson.  She is the oldest living child of a U.S. President following the death of John Eisenhower on December 21, 2013. This is a list of presidents of the United States by age.  The first table charts the age of each United States president at the time of presidential inauguration (first inauguration if elected to multiple and consecutive terms), upon leaving office, and at the time of death.  Each president's lifespan (age at death) is measured in two ways, to allow for the differing number of leap days that each experienced.  The first figure is the number of days between the president's date of birth and date of death, allowing for leap days; in parentheses, the same period is given in years and days, with the years being the number of whole years that the president lived, and the days being the number of days since the last birthday.  Where the president is still living, their lifespan is calculated up to .  The second table includes those presidents who had the distinction among their peers of being the oldest living president, and charts both when they became and ceased to be "oldest living". Jeralean Talley (née Kurtz; May 23, 1899 – June 17, 2015) was an American supercentenarian who was, at the age of 116 years, 25 days, the world's verified oldest living person.  She was previously thought to be the oldest living American, from the death of Elsie Thompson on March 21, 2013 until Gertrude Weaver was verified to be older in July 2014.  Upon Weaver's death on April 6, 2015, Talley was recognized as the oldest living person in the world.  Talley received letters from U.S. President Barack Obama on her 114th and 116th birthdays acknowledging her status. Tulinabo Salama Mushingi (born August 4, 1956) is an American diplomat who currently serves a joint appointment as United States Ambassador to Senegal and United States Ambassador to Guinea-Bissau.  He previously served as the United States Ambassador to Burkina Faso from 2013 to 2016.  He also served in the executive offices of Secretaries of State John F. Kerry and Hillary Clinton.  In February 2017, President Donald Trump nominated Mushingi to serve concurrently as United States Ambassador to Senegal and United States Ambassador to Guinea-Bissau.  Mushingi had originally been nominated for the position by outgoing President Barack Obama in January 2017.  When Trump took office, he withdrew Mushingi's nomination before renominating him for the same position.  He was confirmed by the United States Senate by voice vote on May 18, 2017. Daniel Howard Simpson (born July 9, 1939 in Wheeling, West Virginia) is an American former Foreign Service Officer.  He was the United States Ambassador to the Central African Republic (1990–92), Special Envoy to Somalia and the United States Ambassador to the Democratic Republic of the Congo (1995–98) as well as undertaking other overseas assignments in Burundi, South Africa, Zaire (on three separate occasions) Iceland, Lebanon and Bosnia-Herzegovina.  He also served as the Deputy Commandant of the United States Army War College and on the Board of directors as the Vice President of the National Defense University for the United States Institute of Peace. Vernon A. Walters (January 3, 1917 – February 10, 2002) was a United States Army officer and a diplomat.  Most notably, he served from 1972 to 1976 as Deputy Director of Central Intelligence, from 1985 to 1989 as the United States Ambassador to the United Nations and from 1989 to 1991 as Ambassador to the Federal Republic of Germany during the decisive phase of German Reunification.  Walters rose to the rank of lieutenant general in the U.S. Army and is a member of the Military Intelligence Hall of Fame. Harry Keels Thomas Jr. (born June 3, 1956 in the Harlem section of New York City) is an American diplomat and current United States Ambassador to Zimbabwe.  He served as the United States Ambassador to the Philippines from 2010 to 2013.  A former United States Ambassador to Bangladesh (serving from 2003 to 2005) and Director General of the United States Foreign Service (serving from 2007 to 2009), Thomas was designated by US President Barack Obama on November 19, 2009 to replace Kristie Kenney as Ambassador to the Philippines—the first African American to serve at that post.  He was confirmed by the United States Senate on March 19, 2010 and presented his credentials to Philippine president Gloria Macapagal-Arroyo on April 27, 2010 He was then nominated and confirmed as the United States Ambassador to Zimbabwe on October 22, 2015.  He was sworn in on December 8, 2015. Karen Brevard Stewart (born 1952) is an American diplomat who is the current United States Ambassador to the Marshall Islands.  She was nominated by President Barack Obama to be United States Ambassador to the Marshall Islands on November 5, 2015 was confirmed by the U.S. Senate on May 17, 2016.  Stewart also served as United States Ambassador to Belarus from August 14, 2006 to March 12, 2008 and as United States Ambassador to Laos from November 2010 to August 2013.
Answer: Belgium