His flight to Hungary and rumours about his planned return to Poland were a source of considerable displeasure to his rival Sikorski, now Prime Minister. Sikorski had been in opposition to Rydz-Śmigły and Piłsudski from the time of the 1926 May Coup. Sikorski declared in a telegram to General Stefan Grot-Rowecki, leader of the Armia Krajowa (AK) underground resistance in Poland: "the Polish Government will regard a sojourn of the Marshal in Poland as a sabotage of its work in the country. The Marshal must as soon as possible move to some country of the British Empire". However, Rydz-Śmigły left Hungary on 25 October 1941, and travelling through Slovakia reached Poland. On 30 October, in strict secrecy, he came back to Warsaw to participate in the resistance movement as a common underground soldier, thus voluntarily suspending his rank as Marshal of Poland. He managed to contact Grot-Rowecki, but remained incognito. He died suddenly of heart failure at the age of 55, on 2 December 1941, only five weeks after his arrival in Warsaw. He was buried in Warsaw under his nom de guerre "Adam Zawisza". His tombstone at the Powązki Cemetery bore this assumed name until 1991. A new tombstone inscribed with the Marshal's full name was placed over his grave by the people of Warsaw in 1994.