From Longman Dictionary of Contemporary English(all/only) too true(all/only) too trueTRUEused to say that you know something is true, when you do not like it ‘It’s not as easy as it looks.’ ‘Too true!’ It is only too true that people are judged by their accents. → true
Examples from the Corpus
(all/only) too true• Mr. Waldegrave I fear that on health, as on other issues, that is all too true.• This may be only too true, but if so, why advertise the fact?• It's a cliche to say people are living in fear, but sadly it's all too true in Larne.• Travelers to Prague may find the comparison with Paris starting to ring all too true when it comes to hotel prices. 