well, it was during Sameer and Gayatri's wedding. AT that time, Gayatri was a budding politican under the umbrella of her father. Shruti had already entered Sameer & Gayatri's life by then and has fallen in love with Sameer. Sameer also was in love with Shruti even though Gayatri was his fiance.
Few days before, it was also revealed that Gayatri was actually Om and Parvati;s daughter and SHruti was Gayatri's present parents daughter.
On the wedding day, Gayatri had to leave the house to meet a blackmailer (i forgot the issue on which she was being blackmailed). SInce it was getting very late for the shubh muhurat, Gayatri's mother asked Shruti to fill in for Gayatri for time being until she returned.
The altercation that u mentioned was when Gayatri retd. home and found out that Shruti had actually gone thru the marriage ceremony with Sameer. Sammer was however ignorant to all these facts.