The photo caption listed Ms Trump and the eight other first ladies in attendance but failed to name Gauthier Destenay, the husband of Luxembourg’s openly gay Prime Minister, Xavier Bettel.

Mr Bettel is currently the only openly gay serving world leader.

After drawing condemnation across social media for the “embarrassing” and “disrespectful” omission, the caption was updated to include Mr Destenay, 10 hours after it was originally posted.

The original caption read: “First Lady Melania Trump poses with Belgium’s Queen Mathilde, center, and other spouses of NATO leaders: First Lady Emine Erdogan of Turkey; Iceland’s Thora Margret Baldvinsdottir; the First Lady of France Brigitte Trogneux; First Lady Melania Trump; Slovenia’s Mojca Stropnik; Bulgaria’s Desislava Radeva; Belgium’s Amelie Derbaudrenghien, and Norway’s Ingrid Schulerud, during their visit Thursday, May 25, 2917 (sic), at the Royal Palace in Brussels. (Official White House Photo by Andrea Hanks).”

The photo’s caption named everyone except the husband of Luxembourg openly’s gay Prime Minister. Photo: Andrea Hanks

While some suggested the omission was innocent, many slammed it on social media as “embarrassing” and “disrespectful”.

The photo was taken at last week’s summit in Brussels and was posted to Facebook in a collection of images from Trump’s nine-day international tour.

Mr Trump has previously stated he is “fine” with legislation passed during the Obama administration which allowed couples of the same sex to marry, however Vice-President Mike Pence is known to have strong views in opposition to same-sex marriage.

In a 2006 speech as head of the Republican Study Committee, Mr Pence drew links between marriage law reform and “societal collapse” and claimed refusing to allow gays to marry was not discrimination but an upholding of an idea “ordained by God”.

Trump’s overseas journey ended with an address to US troops in a campaign-style rally in which he declared the tour a “home run”.

Although Ms Trump was twice observed swatting her husband’s hand away when he tried to hold hers during the trip, she praised his efforts in her introduction to the troops.

“My husband worked very hard on this trip and I am very proud of him,” she said.