Question Summary:
Is it permissible to inform a person of his fiancé’s immoral habits?

Question Detail:

 
A very pious, well natured brother sent a proposal for marriage to my friend. This friend of mine who I've known for a long time has a long history of all the wrong things sha has done. She use to drink, take drugs, party, had sexual relation with multiple partner. She was also married once and got divorced after cheating on her husband. I knor for a fact this pious brother doesn't know the truth about her and is completely blind by her beauty. 
Should I say something or leave it the way it is?Technically it's none of my business but it's hard to see someone being misslead to this extend and walking towards a self-destruction.

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salamu  ‘alaykum wa-rahmatullahi wa-barakatuh.
 
Sister in Islam,
Your intention to safeguard the brother in reference from being misled is noble.
Our advice is you approach your friend and express your concern for her. Tell her you love her and wish well for her. The breakdown of the previous marriage was distressing to you and you hope she will make the best of this marriage.
Tell her you want to believe that she changed her lifestyle and the pious person will enhance that.
It is possible your friend may have already discussed her past with her future spouse. Enquire that from her and advise her of the possible consequences of not doing so.
We do not advise you discuss anything with her future spouse.
And Allah Ta’ala Knows Best.
 
Arshad Ali
Student ,Darul Iftaa
Trinidad.
 
Checked and Approved by,
Mufti Ebrahim Desai