Turning out for Girls star Allison Williams' wedding in Saratoga, Wyoming, on Saturday, the pair let their love shine during the romantic event – and didn't shy away from the PDA.
"John and Katy looked happy," the source tells PEOPLE. Though they arrived on separate private jets, "They held hands and sat next to each other during the wedding ceremony."
The musicians, who split in February of 2014, fueled rumors of reconciliation when they stepped out for a double date with Williams and her then-fiancé Ricky Van Veen at the Chateau Marmont in January.
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"They are so in love," a source close to Perry told PEOPLE at the time. "They missed each other."
Perry and Mayer were also spotted getting cozy at a Grateful Dead concert in July.
They were backstage being super sweet together – but not standing too close – in a big group of friends," an onlooker told PEOPLE. "Someone handed her a tie-dyed rose. Katy was extremely polite, gracious and friendly."