Ambassador on a date? What about back problem? (8)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

HE (His/Her Excellency – ambassador) + A D (a date) + a reversal (about) of EH (what) Edit – thanks to  matematico @80 – something got lost here! It’s HE + A D  + a reversal (back) of EH (what) + CA (about)