What is a recognition letter for divorce ? my bf needs it in order to honor his divorced in philippines?

Hi! my boyfriend ( a filipino citizen) was divorced already to his ex wife ( a japanese citizen) . They get married in philippines and then moved in japan since his ex wife is a jap citizen, but theyre relationship failed and eventually filed a divorced in japan. It was acknowledge in japan since divorce is legal their. Now, he went home in the philippines, still a filipino citizen. Their divorced in japan dissolves automatically their marriage in phil because of article 26 (law about mixed marriages) but the local court in phil said that in order to be honored it completely, he needs a "recognition letter" from his wife. My question is what is a recognition letter? what does she need to write their? is it only her personal acknowledgement about their divorce or it is a legal document that can be taken in the city hall of japan? thankyou.... we are planning to get married soon and we want his status to be cleared first, legally. I am a US CITIZEN.