Jennifer Lopez and her ex, Diddy, reunited over Instagram Live for a good cause on Sunday.Diddy kicked off what he called the «world's biggest dance-a-thon» on Sunday — in an effort to raise money to benefit healthcare workers in underserved areas amid the coronavirus outbreak — and he was joined by a number of big stars, including Lopez.The friendly exes chatted and joked around while dancing together virtually over video chat.The star, who joked around with Diddy as they danced, claiming that she «taught» him his moves, also brought over her fiancé, Alex Rodriguez, who appeared to be a huge fan of the rapper.«This man right here is like your biggest fan,» Lopez said of her fiancé, adding that Diddy is one of his «heroes.»After Diddy