it (just) so happens that…
by chance
It just so happened they'd been invited too.
e.g.
/fe3hdialogue/クロード外伝 砂に眠る神話 The Sleeping Sand Legend#61fe7f75bdb0e50000ebc7a7
/fe3hdialogue/Byleth×Caspar#62e54ba4bdb0e50000477933
/fe3hdialogue/Felix×Lysithea#63e7472bbdb0e50000a8002f
/fe3hdialogue/Seteth×Hilda Support Conversations#6179f070bdb0e5000035246f
/fe3hdialogue/Raphael×Leonie Support Conversations#64681f3cbdb0e50000b86301
/fe3hdialogue/軍議・天馬の節/銀雪 War Council: Pegasus Moon (Silver Snow)#63798419bdb0e50000d6b56f