A. (1) The Defendant prepared a loan agreement in the name of C and a written contract to establish a mortgage (hereinafter “instant loan contract”) with the Plaintiff, which is the Defendant’s father, in the name of C, KRW 5 billion on September 25, 2012, KRW 8.5% on the date of credit extension, annual interest, and KRW 8.5% on September 26, 2013 on the date of expiration of the term of credit period (hereinafter “the instant loan contract”). On September 26, 2012, the Defendant prepared a written contract to establish a mortgage (hereinafter “instant mortgage contract”) which establishes a real estate owned by C in order to secure a loan obligation under the instant loan contract, and prepared a written contract to establish a mortgage (hereinafter “instant mortgage contract”) with the content of establishing a mortgage on the instant real estate owned by C in order to secure a loan obligation under the instant loan contract.

(2) On September 26, 2012, the Plaintiff implemented a loan of KRW 5 billion to C in accordance with the instant loan agreement.

B. The instant loan contract and the instant mortgage contract (hereinafter “each of the instant contract”) were forged with the Plaintiff as Seoul Eastern District Court No. 2013Ga103726, which was the Seoul Eastern District Court 2013Ga103726, and C filed a lawsuit seeking the cancellation of the registration of the establishment of the instant mortgage contract on the grounds that the instant loan contract and the instant mortgage contract were null and void. On the grounds that the instant mortgage contract were invalid, the Plaintiff filed a lawsuit seeking the cancellation of the registration of the establishment of the mortgage on the real estate completed in C’s possession pursuant to the instant mortgage contract. On the other hand, the Plaintiff filed a counterclaim with the Seoul East District Court 2014Ga1000, Seoul Eastern District Court 2014Ga1000, and filed a claim for the return of the loan amount equivalent to

(2) On October 12, 2016, the court below held that the defendant participated in the lawsuit as the supplementary intervenor of the plaintiff.