Malcolm Turnbull, "I will deliver a national apology to the survivors, victims and families of institutional child abuse on the 22nd of October".
— Malcolm Turnbull (@TurnbullMalcolm) June 13, 2018
It's unclear on whose behalf Turnbull's apologising.
That wasn't a sufficiently important issue to rate a mention in the press release or the media conference.
But I think it's clear why he's apologising.
Here's an extract from the Hansard for Wednesday, 13 November 2013 - Malcolm Turnbull is delivering a valedictory speech on Kevin Rudd's resignation from the parliament:
When you became Prime Minister, there were quite a few things that we disagreed about, as you know. But your apology to the stolen generation is, as the Prime Minister tonight said, one of those signal moments; one of those moments when a leader is able with his imagination to capture the tenor of the times and make a mark in history, a mark that will never be erased. All of your other achievements—about which we have differing views of course—that your colleagues in the Labor Party have spoken so warmly about tonight, including the handling of the global financial crisis, the National Broadband Network and others, will all pass into forgetfulness. But that apology to the stolen generation will never be forgotten. It is not just one of those marks in the sand of history to be blown or washed away by time, but carved into the granite—into the bedrock—of history. That is your achievement.
It starts at about 1.25 in to this video.