Former German Foreign Minister Guido Westerwelle, the first openly gay leader of a mainstream political party, has died from blood cancer at the age of 54, his foundation said on its website on Friday.Westerwelle was leader of the business-friendly Free Democrats (FDP) from 2001 until 2011 and foreign minister during Chancellor Angela Merkel's second term from 2009 until 2013.His foundation announced in mid-2014 that he had been diagnosed with acute leukemia. He last appeared in public in November, presenting a book on his battle with blood cancer called "Between Two Lives.""We mourn Guido Westerwelle. Our sympathy goes out to his husband and his family," the FDP said in a short statement."I'm lost for words. Guido has fought so hard. The grief is great," FDP leader Christian Lindner said in a tweet.