“…’ , said Dr Mahathir who quit the ruling party he once led last month before going to join an opposition party” reported Amanda Hodge in The Australian of April 11, 2016.

I wonder if he did anything else notable last month or if leading his party was pretty much full time.

“… who last month quit the ruling party he once led to join an opposition party” would be clearer.

Dr Mahathir was Prime Minister of Malaysia for 22 years in the 1980s, 1990s and noughties.