glielo ha detto

told him/her

→ gli lo
phrase Uncommon #14,935
told him/her Glielo combines gli (to him/to her) with lo (it/that). In speech and writing, it is commonly shortened to gliel'ha before ha, as in gliel'ha detto.
IT: Non so chi glielo ha detto.
EN: I don't know who told him/her.

Ha visto che glielo ha detto?

Did you see that he told you?

— Una giornata particolare (1977)

Beh, ha cambiato turno, non glielo ha detto?

Well, he changed shifts, didn't he tell her?

— Hong Kong Express (1994)

Perché non glielo ha detto?

Why didn't he tell him?

Choon Shim dice che glielo ha detto Joo Hwan, e tu dovresti saperne di più.

Choon Shim says Joo Hwan told him, and you should know more.

— Old Boy (2003)

Qualcuno glielo ha detto?

Did anyone tell him?

Chi glielo ha detto?

Who told him?

— Tesis (1996)

Deve smettere di fumare, glielo ha detto anche il dottore.

He has to stop smoking, the doctor told him too.