It depends, the payer can claim the mortgage interest deduction IF he/she is also LIABLE for the mortgage. If you were not a signer on the mortgage you are not liable for the loan.
Here below is a helpful excerpt from page 9 of IRS Publication 936 Home Mortgage Interest Deduction.
"If you and at least
one other person (other than your spouse if you
file a joint return) were liable for and paid interest
on a mortgage that was for your home, and
the other person received a Form 1098 showing
the interest that was paid during the year, attach
a statement to your return explaining this.
Show how much of the interest each of you
paid, and give the name and address of the person
who received the form. Deduct your share
of the interest on Schedule A (Form 1040),
line 11, and print “See attached” next to the line.
Also, deduct your share of any qualified mortgage
insurance premiums on Schedule A (Form
1040), line 13".
Click on this link for further information about Mortgage Interest Deductions: https://www.irs.gov/pub/irs-pdf/p936.pdf
